Multisize
me
Grading a knitting pattern for
multiple sizes
You've designed a new
sweater, and you'd like to publish the
pattern. The only trouble is that you've
only designed it to fit one size: yours.
Now what?
Presumably by this point,
what you have is a set of notes or pattern
instructions for one size. You worked them
out, perhaps, by trial and error, or by
computation and tweaking as you go. In
fact, even if you do characterize your
design technique as trial and error, your
design was probably still underscored by
certain fundamental calculations: how many
stitches to cast on here, the circumference
of the sweater there, and the length between
the two points. (If you don't have any
notes or instructions jotted down for your
prototype garment, sorry, can't help you
there: you'll need to work backwards to
figure out the key measurements, stitch
and row counts for your original garment.
And then, if you want to make a habit of
replicating or multisizing your patterns
for others, change your notetaking habits!)
Given this starting point,
grading your knitting pattern for other
sizes amounts to three steps that should
sound somewhat similar to what you just
did:

Figure out the
key finished measurements of the
original garment, and the ease involved
for each of these measurements.

Determine what these
key finished measurements will be for
each size of the pattern.

Compute the stitch
and row counts for each of these measurements.

Insert these numbers
into your written instructions, tweaking
as necessary.
These four steps might
sound a little simplistic, but in reality,
multisizing a pattern is just more arithmetic
and logic piled on top of the arithmetic
and logic you used the first time around.
If you were able to figure out instructions
and numbers for one size, you can do it
for another.
Of course, the process
isn't always that simple. Sometimes,
the truly hard part is figuring out what those
other sizes should be. Other times, the
construction method or design details of
the garment throw a monkey wrench into
the computations.
How do I know
what sizes other people are, anyway?
This is the milliondollar
question, isn't it? How do you find a set
of sizes that will fit all knitters, from
extraextraextrasmall to doubleventi?
It's
all very well to fit yourself and tailor
the number of stitches and rows to your
own body as you knit, but the general
idea of a knitting pattern is that complete
instructions are provided for the knitter
to follow to arrive at a finished product.
This doesn't mean that the knitter doesn't
think while following instructions, but "increase until it's
big enough to fit around your chest" isn't
a pattern instruction  it's just the
intended result. Even if you do empower
the knitter to recognize where adjustments
can be made, and how to make them, the
knitter still (quite fairly) has some expectations
that you'll provide numbers for each pattern
size. The knitter also hopes that you'll
also cover the size that he or she wants
to knit.
However, there is no
set of standards that will apply satisfactorily
across a broad range of sizes. (If there
was one, clothes shopping experiences would
probably be more pleasurable.) There are
standard sizing guides out there, and they
may or may not be the right fit for you
and the knitter of your patterns. For example,
there are the Craft Yarn Council of America's sizing
standards, which are used by some knitting
publications; other publishers may have
different sizing guides. You can also obtain
sizing information in some knitting or
sewing reference books, or from various
standards organizations (but be prepared
to pay for it), or from digging into the
data used by knitting software programs
(more on that later). You can even do your
own detective work and survey readymade
clothing, sewing patterns, or neighbourhood
children.
Standards and guides,
though, are based on statistical averages
and assumptions: for example, standards
often presume that a woman has a B cup,
and that on average, there are height differences
between sizes (a woman with a 32 inch bust
is presumed to be shorter than a woman
with a 40 inch bust). In the aggregate,
these presumptions are fairly made, but
it means that no sizing methodology will
ever truly account for the ways of all flesh
and where it's located. A full bust measurement
of 36 inches could belong to a smallboned
woman with a C or D cup, or to a woman
who perfectly matches the measurements
in a published standard  yet, these women
would probably have different crossshoulder
measurements, sleeve lengths, back waist
lengths, and hip and waist measurements.
If you conduct your own research to develop
your own size guidelines, your data will
suffer from the same flaws of your source.
If the clothing lines you inspect tend
to be designed for skinnier bodies, or
if the pattern line is reputed to fit too
tightly in the shoulder area, you may wind
up importing those problems into your patterns.
Even guides published in reference books
will become outdated with time, as average
adult height and weight increases over
decades. On top of that, some of these
standards or guides may lack some dimensions
that you need for your grading work. Some
guides are complete; for others, you may
have to fill in some details yourself.
Despite all of these
issues with standards and size guides,
you will still need to have a starting
point to assist you in grading your pattern
up and down, and that starting point will
probably be somebody else's sizing charts.
At a minimum, for grading a woman's pullover,
you'll want to find a table that correlates at
least these measurements:

full bust circumference
(assuming that the body shape reflected
in these measurements has a B cup)

crossshoulder (shoulder
point to shoulder point)

wingspan (from wrist
to wrist, arms slightly bent, across
the shoulders)

back waist length
(from back neck to waistline)

waist circumference

hip circumference

hip depth (from waistline
to hipline)
Some tables will express
wingspan in a different way: they may give
a halfwingspan value (from center back,
over the shoulder, then down the slightly
bent arm to the wrist), or they may give
a sleeve length (from shoulder point to
wrist) plus a crossshoulder measurement.
In theory, twice the sleeve length
plus the crossback measurement should
equal the total wingspan. If you find a
data set that doesn't quite add up this
way, then either the sleeve length was
made longer to ensure wrist coverage when
the arm is bent sharply, or the shoulder
point used to determine the sleeve length
is not the same shoulder point
used for the crossshoulder measurement.
This can lead to confusion when drafting
setin sleeves.
These are the basic measurements,
but if you've ever tried to grade a pattern,
you can probably think of additional data
that you'd love to have:

armhole depth (vertical
distance between shoulder and armpit)

raglan depth (diagonal
distance between crew neckline and
armpit)

bicep circumference
(measured around the fullest part of
the arm)

wrist circumference

head circumference
(although this is obviously useful
for hats, it's also useful to know
whether a neckline will stretch enough
to fit over the wearer's head)

neck width (not neck
circumference, but the horizontal distance)
This data is out there
(particularly the last three items), but
information about depths and biceps can
be harder to come by; one reason is because
these dimensions, when they exist, are
often expressed in terms of finished garment
measurements, which are heavily influenced
by the design and wearing ease of the garment,
and not in terms of actual body measurements.
You should make a note, by the way, whether
the dimensions in your sizing standard
are finished measurements, or actual body
measurements.
Range and depth:
selecting the sizes
There are two aspects
to selecting a size range for a pattern.
The first, which is the most obvious, is
choosing the range of sizes: what
is the smallest size? What is the largest
size?
We won't go into the
politics of offering a garment in a range
of sizes. It is probably an objective truth
to say that not every clothing design will
flatter every figure, but what a designer
does with that truth is a personal (and
business) choice. Some designers may consider
that their design integrity is compromised
if a pattern is adjusted to fit a body
shape for which it was not intended. Other
designers, however, figure that they cannot
be the judges of what will look good on
a body that they have never seen, and realize
that the customer knows what he or she
wants.
The second aspect is
the number of sizes within the
range. If you are offering sizes ranging
from a 32 inch to a 62 inch full bust measurement,
do you need to offer sizing in increments
of two inches? Four? Six? The choice of
increment could have you crunching numbers
for six or sixteen sizes.
When
a pattern is published by a third party,
the designer (here, when we use the term "designer",
we're not only referring to the person
who greated the design and perhaps first
prototype, but also to the pattern writer
who creates the instructions for different
sizes  these roles may be filled by
the same or different people) may or
may not have any say about the range
or number of sizes. A publisher may expect
instructions for a specific range and
number of sizes, which relieves the designer
of the burden of decisionmaking. But
in a selfpublishing situation, it's
up to the designer to decide how many
sizes to offer, and over what range.
These decisions may be constrained by
space and publishing considerations (there
is a cost to having instructions reviewed
by technical editors, or having multiple
sizes test knit). However, other design
considerations may impact the choice
of size increment:
Ease:
is the garment intended to fit loosely,
or snugly? A loosefitting garment is usually
a little more forgiving; with an intended
ten inches of ease in the body, it will
probably not matter if the wearer has a
40 or a 43 inch chest as much as it would
if the garment was intended to be tightfitting.
Scope for adjustments:
is it easy for the knitter to make his
or her own adjustments without significantly
altering the pattern, and if so, is it
possible to provide fewer sizes along with
instructions on finetuning the fit?
Whether
you can "cheat" this
way will depend on the garment style and
patterning. Provided some guidance was
included in the pattern, it would probably
be easy for a knitter with a small amount
of experience to alter the size of a raglan
pullover by an inch or two. But it wouldn't
be so easy if the pullover involved an
allover stranded colourwork pattern that
would be cut off at the wrong point if
the stitch counts were changed. This kind
of decision requires some consideration
 the knitter may or may not appreciate
being given this much latitude.
These two factors are
related. Let's consider an example of a
pullover to be offered in sizes to fit
bodies measuring 30 inches to 60 inches,
full bust measurement.
If the garment was intended
to fit rather loosely, like a dropshoulder
sweater, experience might suggest that
the pullover would look just as good with
six inches of ease as with ten inches of
ease. Is it necessary to provide pattern
instructions at 2inch increments? Likely
not, given the loose fit, and here is why:
With such a range of
tolerable ease for a given size, there
will be some overlap between sizes. For
a 36 inch full bust measurement and between
6 and 10 inches of ease, the finished size
of the garment could be 42 to 46 inches
(we could also express this as 44 inches,
plus or minus 2 inches). For a 38 inch
full bust measurement, the finished size
of the garment could be 44 to 48 inches
(or 46 inches, plus or minus 2 inches),
and for a 40 inch full bust measurement,
the finished size of the garment could
be 46 to 50 inches (or 48 inches, plus
or minus 2 inches).

For
a sweater that can tolerate between
6 to 10 inches of ease, you can see
that there will be overlap in the
range of acceptable finished garment
sizes for these three "adjacent" body
sizes. 
Note that the appropriate
finished sizes for the 38 inch bust size
are covered by the potential ranges of
the 36 inch and the 40 inch sizes, and
in fact the smallest finished size for
the 40 inch bust measurement is also the
largest size for the 36 inch full bust
measurement.
If we provided instructions
for every 2 inch increment for this design,
we would have to provide instructions for
a full bust measurement of 30, 32, 34,
36, 38, 40, 42, 44, 46, 48, 50, 52, 54,
56, 58, and 60 inches: sixteen sizes. But
given the overlap between sizes 36 and
38, and 38 and 40, it seems that we could
perhaps drop every other size, and still
provide the knitter with decent coverage.
We would then be left writing up instructions
for full bust sizes of 30, 34, 38, 42,
46, 50, 54, 58, and... well, the original
intention was to end at 60 inches, so you
could either provide the 60 inch size,
and respace the sizes between 30 and 60
(or not). Alternatively, you may choose
to either end with 58 or 62 instead. At
least, if we choose a final size for a
62 inch full bust measurement, we now have
only nine sizes to write up instead of
sixteen.

Even
if the size 38 pattern instructions
are omitted, the size 36 or the size
40 instructions will cover the wearer
between these two sizes. 
The rule that we just
followed in this example is to increment
the body sizes by an amount equal to the
range of acceptable ease. Here, we
had 4 inches of leeway in the ease (6 to
10 inches of ease); we could therefore
increment the sizes by 4 inches (e.g.,
for a body measurement of 36 inches, to
40, to 44, to 48, etc.). With this 4inch
increment, an appropriate amount of ease
will be available for any wearer with a
full bust measurement betwen 30 and 62
inches  even if the wearer falls between
two of the pattern sizes.
When we actually choose the
finished dimensions for each size, we would
logically choose to add 8 inches of ease
 the midpoint between the 6 and 10 inches
of acceptable ease.
Full bust measurement (inches) 
30 
34 
38 
42 
46 
50 
54 
58 
62 
Finished garment measurement (inches) 
38 
42 
46 
50 
54 
58 
62 
66 
70 
But if the garment was
intended to have a slinky, tight fit 
say, 0 to 1 inch of wearing ease (every
fitting style can admit some flexibility
in ease, whether it ranges from 0.5 to
+0.5 inches, or 0 to 1 inches)  then
incrementing the sizes by four inches would
leave some gaps.

In a
garment style with little tolerance
for ease variation, providing pattern
instructions in large increments
leaves a number of sizes uncovered. 
However, if we follow
the same rule as above  that we increment
the sizes by an amount equal to the range
of acceptable ease, which here is 1 inch
 we would have to generate instructions
for thirtyone sizes. Even if
this would make every knitter happy, that's
a crazy number of sizes to work into a
single pattern.
If you are determined
to provide all available sizes in one pattern,
you'll need to make a judgment call: provide
all possible sizes, or drop some sizes
and leave them as an exercise to the reader?
This is where the second consideration,
scope for adjustment, comes in; it could
be that if the garment design is simple
enough to allow knitters to easily alter
the garment size by an inch or two, you
can omit some sizes and leave it to the
knitter to tweak the sizing. If at all
possible, though, make this alteration
option abundantly clear in the pattern
instructions.
Numbercrunching:
applying theory to practice
Now, you've got your
target body measurements for each size.
You've figured out the increments for your
pattern sizes, and you've also managed
to determine the finished garment size
(the full bust measurement, at least) for
each garment size.
Now for more arithmetic!
After the anguish of locating an appropriate
sizing standard and determining the range
of sizes to provide, this part should seem
easy.
Figure out the
key finished measurements of the original
garment, and the ease involved for each
of these measurements: You can
likely characterize your prototype pattern
as a set of key finished measurements
 the circumference at the hem, waist,
and bust; the width at the shoulders;
the depth of the armhole and the front
and back neckline, and so forth. Based
on those finished measurements, you will
have also worked out the amount of wearing
and design ease. Write these things down:

Some
possible key finished measurements
and ease amounts for the original
pattern. 
One important point to
consider is whether your prototype fits
within the sizing guide that you intend
to follow. If the prototype was made for
you, for example, and you are unusually
longwaisted or are very smallboned, it
may be that you will need to tweak your
prototype measurements to fit your sizing
standard. Your original measurements, though,
will provide a guide as to how much ease
to add to all the different measurements:
ease at the bust, around the wrist, across
the shoulders, and so on. These amounts
of ease will likely remain fairly constant
across all sizes; you might, with your
own personal fitting philosophy, choose
to vary the amount of ease for some size
ranges, but the original amount of ease
for each measurement of your prototype
will be your guide.
Finished lengths may
be treated differently. The neckline depth
at front and back will likely be fairly
constant across sizes, although as sizes
increase you may wish to increase the front
depth of a crew neck to ensure there is
ample room for the neck, and of a Vneck
or other decorative neckline to maintain
design proportions. The shoulder height
(the vertical distance created during shoulder
shaping) will likely also be fairly constant;
while some people have shoulders that slope
more or less than the average (whatever
average is), you can't really anticipate
this in a knitting pattern.
Some length measurements
require a little more planning. Sizing
standards will tell you that the back waist
length will increase with size; the overall
length of a garment, therefore, will theoretically
increase by the amount that the back waist
length increases. However, the design of
the garment (if there is a specific vertical
pattern repeat that is used) may prevent
you from providing instructions in such
increments; you might need to fix a single
length for every size, so that your Fair
Isle pattern or your cable panels begin
and end at the right place. Also, looking
at your schematic, you will realize that
there are two places where length can be
added to the garment: below and above the
underarm. As you increase in size, you
may find that you will be increasing the
armscye depth, so you may not need to make
any adjustments below the underarm. Similar
logic may apply to the sleeve cap depth
and the sleeve length between wrist and
bicep.
Determine what
these key finished measurements will
be for each size of the pattern: Perhaps
the most obvious way to work this out
is to construct a table for yourself
 either by hand or using a spreadsheet
program, if you are so inclined  so
that you can fill in the key finished
measurements for each of your intended
sizes. If you are more of a visual person,
you might consider sketching a pattern
schematic for each size, and writing
numbers on the schematic.
Below is an example of
a table for a relatively simple setin
sleeve pullover, knit flat with a separate
front and back, with no waist shaping and
four inches of ease at the chest (remember,
that's two inches for each of the front
and back). Each column corresponds to a
size of the pattern, and each row corresponds
to a finished measurement of the
garment. The one column of numbers that
is filled in corresponds to the one set
of numbers you know at this time: your
prototype. For ease of reference, the table
also includes the amount of planned ease:

Ease 
Size 34" 
Size 38" 
Size 42" 
Size 46" 
Width at hem 
(see chest) 
 
 
23 
 
Width at chest 
2 
 
 
23 
 
Crossshoulder width 
0.25 
 
 
15.5 
 
Length from hem to underarm 
(same length,
all sizes) 
 
 
16 
 
Shoulder height 
(same length,
all sizes) 
 
 
0.75 
 
Vertical armscye depth 
 
 
 
8 
 
Front neckline depth 
 
 
 
6 
 
Back neckline depth 
(same length,
all sizes) 
 
 
1 
 
Neckline width 
 
 
 
7 
 
Width at wrist 
1.5 
 
 
9 
 
Width at bicep 
3 
 
 
18 
 
Length from wrist to bicep 
 
 
 
20 
 
Sleeve cap depth 
 
 
 
6 
 
Some
of the "ease" values,
particularly length measurements (which
aren't really "ease") might be left blank,
depending on how things need to be adjusted
based on finished lengths; also, for some
values you might not actually know the
amount of ease, but only the finished dimension
 for example, if your armscye depth might
be drawn from a sizing guide that provides
finished measurements, and not the underlying
body dimensions. For each size column,
the empty cells will need to be filled
in with a number, which will be derived
in part from the ease that you intend to
insert for each measurement, and from your
sizing guide.
It may be that your prototype
measurements and your pattern sizes fall between the
sizes in the standard you're following;
for example, your standard may give dimensions
for full bust measurements of 36, 40, and
44 inches, whereas you are intending to
provide pattern sizes for 38, 42, and 46
inches. In that case, you will need to
interpolate or extrapolate from the numbers
you have in order to fill in this table:
for example, if your standard said that
a wrist measurement for a size 36 is 7
inches, and for a size 40 is 7.25 inches,
it would be fair to conclude that the wrist
measurement for a size 38 is 7.125 inches.
You will therefore be
able to gradually fill in these numbers
(in this example, the numbers are fictional):

Ease 
Size 34" 
Size 38" 
Size 42" 
Size 46" 
Width at hem 
(see chest) 
19 
21 
23 
25 
Width at chest 
2 
19 
21 
23 
25 
Crossshoulder width 
0.25 
15 
15.25 
15.5 
15.75 
Length from hem to underarm 
(same length,
all sizes) 
16 
16 
16 
16 
Shoulder height 
(same length,
all sizes) 
0.75 
0.75 
0.75 
0.75 
Vertical armscye depth 
 
7.5 
7.75 
8 
8.25 
Front neckline depth 
 
5.5 
5.75 
6 
6.25 
Back neckline depth 
(same length,
all sizes) 
1 
1 
1 
1 
Neckline width 
 
6.5 
7 
7 
7 
Width at wrist 
1.5 
8.5 
8.75 
9 
9 
Width at bicep 
3 
16 
17 
18 
19 
Length from wrist to bicep 
 
19 
19.5 
20 
20.5 
Sleeve cap depth 
 
5.5 
5.75 
6 
6.25 
Compute the stitch
and row counts for each of these measurements: This
is a matter of converting your numbers
to stitches or rows, based on your gauge.
In some instances, you may need to round
up or down to the nearest even or odd
number in order to maintain symmetry
in your design; if you need to have a
central stitch on each body piece, for
example, then you will need to make sure
that all of your stitch counts for the
body are odd. Here, our fictional design
has a gauge of 5 stitchs and 7 rows per
inch, and it doesn't matter whether the
sleeves have an even or odd number of
stitches, but it does matter that we
have an even number of stitches on each
of the front and back:

Ease 
Size 34" 
Size 38" 
Size 42" 
Size 46" 
Hem 
(see chest) 
96 sts 
106 sts 
116 sts 
126 sts 
Chest 
2 
96 sts 
106 sts 
116 sts 
126 sts 
Crossshoulder 
0.25 
76 sts 
76 sts 
78 sts 
78 sts 
Hem to underarm 
(same length,
all sizes) 
112 rows 
112 rows 
112 rows 
112 rows 
Shoulder height 
(same length,
all sizes) 
6 rows 
6 rows 
6 rows 
6 rows 
Vertical armscye depth 
 
52 rows 
54 rows 
56 rows 
58 rows 
Front neckline depth 
 
38 rows 
40 rows 
42 rows 
44 rows 
Back neckline depth 
(same length,
all sizes) 
8 rows 
8 rows 
8 rows 
8 rows 
Neckline width 
 
32 sts 
34 sts 
34 sts 
34 sts 
Width at wrist 
1.5 
43 sts 
44 sts 
45 sts 
45 sts 
Width at bicep 
3 
79 sts 
84 sts 
91 sts 
95 sts 
Length from wrist to bicep 
 
134 rows 
136 rows 
140 rows 
144 rows 
Sleeve cap depth 
 
38 rows 
40 rows 
42 rows 
44 rows 
You'll note that because
of the restriction that the front and backs
each have an even number of stitches, we've
had to make a change: 5 stitches per inch,
times 19 inches, equals an odd number (95).
Here, we've increased the stitch count
by one. Given that the pieces of this garment
are knit flat, a seam allowance will be
needed anyway. Even after taking a conventional
onestitch allowance for seaming, the final
width will be very close to the intended
finished width.
You'll also note that
other values, like the cross shoulder width,
no longer increase with each size  an
effect of rounding off to a convenient
stitch count. Here, values were rounded
down to the nearest even number to try
to ensure that the seamline between the
body and sleeve stays as close to the shoulder
point as possible; however, you might choose
to round up, particularly if the garment
was meant to have an easy fit.
Also, lengths such as
the armscye depth or neckline depth may
be rounded off to a convenient even number,
even if the accurate value is an odd number
of rows. Although it's not necessary to
do this, often knitting patterns provide
lengths in terms of even numbers of rows,
so that the next stage of shaping always
begins on a rightside row. (This presumes,
of course, that the work began on a rightside
row, too.) This is not mandatory 
it's only a convention, of sorts, and is
not as conventional as other "rules", such
as the direction in which a chart is read.
Finally, note that even
though it might not matter whether stitch
counts for the sleeve are odd or even,
they need to be consistently odd
or even for each size(assuming your sleeve
is symmetric, and not tailored closely
to actual body shape  which isn't symmetric).
This is an adjustment you might make at
this stage, or during the "tweaking" stage
when you insert the numbers into your written
instructions. (Here, we've already made
that adjustment.)
Insert these
numbers into your written instructions,
tweaking as necessary: Your pattern instructions are the instructions that get you from one of these finished measurements to another. For example, if your prototype notes told you (for the 42 inch size) to increase from 45 stitches at the wrist to 91 stitches at the bicep over 140 rows, then you might have written these instructions as:>
Increase 1 stitch each side
every 6 rows 23 times; work 2 rows even.
You would then figure
out something similar for all of the other
sizes.
For the 34 inch (body
measurement) size, you need to increase
from 43 stitches to 79 stitches over 134
rows:
Increase 1 stitch each side
every 7 rows 18 times; work 8 rows even.
Another convention is
to space increases so that they always
fall on the right side of the work  in
other words, to specify that increases
are worked every 6 or 8 rows, but not every
seven. You may choose to follow this convention
if you wish. One example:
Increase 1 stitch each side
every 6 rows 9 times, then every 8 rows
9 times; work 8 rows even.
For the 38 inch size:
Increase 1 stitch each side
every 6 rows 20 times; work 16 rows even.
For the 46 inch size:
Increase 1 stitch each side
every 5 rows 25 times; work 19 rows even.
Alternatively, because
it may not be desirable to have 19 rows
worked even at the end, but to have them
spaced out a little more:
Increase 1 stitch each side
every 5 rows 15 times, then every 6 rows
10 times; work 9 rows even.
Having figured this out,
you'll then need to merge all of these
instructions  how confusing you wish
to make your pattern instructions is up
to you. One example, using the more complex
instructions for the 34 and 46 inch sizes:
Increase 1 stitch each side
every (6, 6, 6, 5) rows (9, 20, 23, 15)
times, then every (8, 0, 0, 6) rows every
(9, 0, 0, 10) times; work (8, 16, 2, 9)
rows even.
The exact format will
depend on the formatting standards dictated
by the publisher, if you are not publishing
the pattern yourself.
This is a simple example;
you can imagine that when you work out
the shaping instructions for more complex
shapes, like sleeve caps, armscye shaping,
and necklines, that compressing the instructions
into concise statements may be more of
a challenge. Clear pattern writing takes
some skill!
As you work out these
instructions, the need to tweak the numbers
you had computed will arise. One of the
tweaks you will need to consider is a seam
allowance: do you need to add extra stitches
for seams? If you have a neck finish or
a ribbing that requires a specific multiple
of stitches, will the numbers you've computed
work, or do you need to change the numbers
or sneak in some increases or decreases?
Changes like these make pattern writing
a somewhat iterative process; although
you will have worked out some numbers in
the previous step, those numbers might
have to change, and you may need to recompute
some other measurements to confirm that
your instructions will still yield pieces
of the correct dimension.
It may also be that the
garment design imposes restrictions on
the possible sizes: think of an Aran sweater
composed of specific cable panels that
are all three inches wide, and that need
to be centered on the front and back 
while the obvious answer to multisizing
is to increase each size by 12 inches (two
panels each on the front and back  that's
rather a lot!), other creative solutions
are available to cover intermediate sizes.
Next time: Dealing
with restrictive design considerations;
estimating yardage amounts; and using knitting
pattern software.
References
Find Knitty's sizing
guides here,
based on the CYCA guidelines, and a link
to Ysolda Teague's expanded guide that
provides what the CYCA information is missing.
You can also consider
references like Righetti's Sweater
Design in Plain English (St Martin's
Griffin, 1990), which includes reference
tables for men, women and children.
Other measurement sources
include standards bodies, such as ASTM
International. Reference D5585, for
example, is a standard table of body measurements
for adult female misses, sizes 220 (32
to 44.5 inch full bust measurement); D6960
covers sizes women's plus sizes 14W to
32W (39.5 to 57.5 inch full bust measurement).
ASTM data includes values such as the armscye
girth (around the armscye, front and back)
as well as armscye ("scye") depth), and
upper arm girth.
However,
as cautioned above, all data has its
flaws, and despite the fact that the
size guide you use is called a "standard",
you may find that the data is not representative
of the knitters of your patterns. 