Further ruminations on ease

This was cut (by me) from the last Knitty article, because as usual I went on and on and on. And on.

On the subject of wearing ease versus design ease, in the article I stated that the wearing ease across garment sizes (assuming that the other garment characteristics, such as the type of fabric and style, stay the same) is consistent, but that this rule doesn’t apply to design ease. Here’s my explanation.

Wearing ease is an absolute value, all other things being equal
Wearing ease adds extra breathing and moving room around the body so that the garment can be worn comfortably, and move the way the wearer needs it to move. Operating on the totally unscientific assumption that bodies expand and contract approximately same amount when breathing or whatever (what do I look like, a physiologist?), the amount of extra space that a woman (or man, or child) needs around the body for those basic functions is just about the same — or at least, the variation from person to person is not as radical as the variation between absolute body sizes at rest. (Remember, I’m not talking about the length of a garment piece–a larger bra cup size, for example, needs more length over the bust to prevent riding up–I’m talking about girth right now.)

To look at it in pictures, whether you’re small or large, I’m saying you need a set amount of wearing ease, while the design ease is not a fixed amount. Here’s a cross-sectional view of a couple of torsos (just pretend we’re elliptical), with the wearing ease I’m talking about:

The torso is solid; the hatched area is the space between the torso and the garment. That space is the wearing ease, and you see it is roughly the same width for both the small torso on the left and the large torso on the right.

Now, how does that translate into real numbers? You might think that this must mean that wearing ease must somehow be proportional to the torso measurement, for example, an additional 5% or 10% added to the torso girth. That’s not correct. In fact, in the diagram above, we’ve added an absolute amount of wearing ease, and the amount of “space” it has added is the same.


Let’s try to prove this mathematically using the simpler case of a circular cross-section. (Of course our torsos don’t look like this. This is a simplified example.)

The circumference of a circle is equal to πd, where d is the diameter of the circle. This could also be expressed as 2πr, where r is the radius of the circle. Of course you knew this.

Now, say we had circles reflecting two body sizes: the small with a full bust measurement of 32 inches and the large with a full bust measurement of 48 inches. Let us say also that we have a garment designed to have 6 inches of wearing ease. For the small, that gives the garment a total of 38 inches around the bust. For the large, that’s 54 inches. Here’s what it would look like–and these figures are to scale:

The amount of “space” between the torso and the garment looks the same, doesn’t it? In fact, it looks like that first illustration of a constant amount of wearing ease for two different sizes.

You can prove it algebraically, if you want:

Circumference of the garment, including ease = C

Circumference of the body only = c

Amount of ease between the body and the garment (which we assumed was 6 inches in the above case) = E

Radius from the center of the body to the garment line = R

Radius from the center of the body to the circumference of the body = r

This means that the distance between the garment and the body, x in the diagram below, is Rr.

First, clearly C = c + E. The circumference of the garment is the circumference of the body, plus the ease. In our example above, 38 inches = 32 inches plus 6 inches.

Next, C = 2πR. This equation relates the garment radius to the garment circumference.

Then, c = 2πr. This equation relates the body radius to the body circumference.

But because we know that C = c + E, we can combine those second two equations:

R = 2πr + E

And we can rearrange this expression:

E = 2πR – 2πr

or

E = 2π(Rr)

But hey, the distance between the garment and the body in our diagram above is x, which is Rr. In other words:

E = 2πx

What does this mean? This means that the amount of space, x, between the garment and the torso in our cross-sectional view is always directly proportional to the wearing ease E. It is completely independent of the actual value of r, the torso radius. In other words, it doesn’t matter whether you’re an XXS or an XXL size: 2 inches of ease will give you the same amount of space x between your body and the garment.

In short, what I’m attempting to demonstrate by this exercise is that if you want a 1 inch gap of wearing ease between your body and the garment all the way around, you’ll be adding the same amount of extra fabric regardless of your size. It doesn’t matter whether you’re a 32AA or if you’re a 48DDD. That’s all. (Yes, bust shaping matters if you’re a 48DDD as opposed to a 32AA, and if the garment incorporates waist shaping, the slope of the increases from waist to underarm will be affected by the length of your torso, the garment measurement at the waist, and whether you’re 48 or 32 inches around at the fullest point. But I’m just talking about wearing ease here.)

Some number crunching, again based on the circular cross-section approximation, to prove this point:

for a 2 inch gap between the body and the garment
body
circumference
c
body radius
r
garment radius
R (that’s r plus 2)
garment
circumference
C = 2πR
ease
Cc
30 inches 4.77 inches 6.77 inches 42.54 inches 12.6 inches
34 inches 5.41 inches 7.41 inches 46.56 inches 12.6 inches
40 inches 6.37 inches 8.37 inches 52.59 inches 12.6 inches
48 inches 7.64 inches 9.64 inches 60.57 inches 12.6 inches
58 inches 9.23 inches 11.23 inches 70.56 inches 12.6 inches

In other words, for any body, 12 inches of ease will always result in a gap of two inches between the body and the garment.

Some refinements to this simplistic model:

  1. No garment hangs such that the body is perfectly centered underneath. The clothing hangs from the shoulders, and pretty much lies directly on the shoulder blades and upper chest. Much of this ease winds up being concentrated at the sides, especially under the arms. Around waist level, where the body is tapered in from the chest, the ease is distributed a little more evenly.
  2. The body does not have a circular cross-section. The upper arm, maybe, but not the torso. The torso is closer to an ellipse, which is more difficult to model. The ellipse doesn’t have a single radius or diameter; it has a major and minor axis that defines the “width” and “length” of the shape. The perimeter of the ellipse is dependent on both those values. However, if an approximation of the ellipse perimeter (I say approximation, because otherwise it involves integrals) is reduced to the case where the “width” of the ellipse is proportional to its “length” (for example, if we assumed that bodies are always twice as wide as they are thick), we wind up with a directly proportional relationship between perimeter and “width” (or “length”), which means that the same argument above will hold: X inches of ease will always result in a gap of Y inches between the body and the garment, regardless of your actual size.
  3. There is actually less ease than these numbers suggest, because of the thickness of the actual fabric. Hand knit fabric typically has significant thickness to it, from maybe 1/16 (baby weight range) to 1/4 (bulky) of an inch, and that thickness has to go somewhere. It doesn’t really all lie “outside” the schematic garment measurement–if the garment apparently measures 36 inches around, that means the thickness of the fabric is within the 36 inch perimeter, which means that the actual “space” between the body and the garment is reduced. Where you might have had an apparent 2 inch gap, as in the model above, you really might in fact have only had a 1 3/4 inch gap.

Now, that’s the case for showing that wearing ease is an absolute number: a fixed amount of ease for a range of sizes will result in the same “gap” between clothing and body. Conversely, we can also examine the argument for proportional ease, and demonstrate that wearing ease doesn’t work that way.

Wearing ease is not calculated as a proportion of the body size
If wearing ease were not an absolute value, as I’ve postulated, then it must somehow be proportional to the body size. For example, one could imagine a rule that for a comfortable fit, a set-in sleeve sweater knit in aran weight yarn must have at least 12% ease (this would be equivalent to saying that a woman with a 33 inch full bust measurement needs 4 inches of ease–a total of 37 inches at the fullest part of the garment–to feel comfortable). With that fictional rule, we’d conclude that:

assuming a fictional 12% wearing ease rule
for a full bust measurement of… the proportional ease would be…
30 inches 3.6 inches
34 inches 4.1 inches
40 inches 4.8 inches
48 inches 5.8 inches
58 inches 7.0 inches

In other words, if the full bust measurement of the wearer increases by 50%, then under this rule you must add 50% more wearing ease as well. It does sound logical, but does it actually make physical sense? Comparing the small and the large sizes in this table, we’d have this:

The distance between the garment and the body is now less for the smaller body than it is for the larger body. In essence, using a proportional relationship like this implies that a smaller body should be comfortable wearing tighter clothes. Don’t confuse “comfortable” with “looks more attractive”–we’re talking about wearing ease, not a question of what size person should wear tight-fitting clothing.

If it were true that a smaller body is just as comfortable wearing clothes with less wearing ease, that means if a woman with a 42 inch full bust measurement is just comfortable in a bulky-knit, set-in sleeve sweater measuring 46 inches around (ease of 4 inches, or 9.5% of the full bust measurement), then logically a woman with a 32 inch full bust measurement should be comfortable wearing a bulky-knit, set-in sleeve sweater measuring 35 inches around (proportional ease of 9.5% is equal to 3 inches). I can tell you that this conclusion is not true. In a set-in sleeve sweater, that’s sweltering and constricting. Remember, the fabric itself consumes some of that apparent ease, which brings the garment even closer to the body. And any seam ridges within the garment are the same depth, regardless of garment size.

If you’re argumentative, you could say that this distinction comes down to the way one defines terms like “space” and “ease”. That’s true–is ease supposed to be the volume of space between the body and the garment (a three-dimensional measure), or is it supposed to be the area between the body and garment at a given cross-section (a two-dimensional measure), or is it supposed to be the linear (one-dimensional) difference in circumference between the torso and garment? Commonly, wearing ease is treated like the one-dimensional difference.

You could also say that in the range of numbers we’re working with, an extra inch or two around the torso of a larger body isn’t going to make a whole lot of difference. That’s also true too, but not because that extra inch or two doesn’t make a difference to the wearing ease, but because the extra “space” that’s not needed for wearing ease gets absorbed into the design ease of the garment.

Design ease, on the other hand, is not absolute–it’s proportional
Whatever extra fabric exists in the garment that isn’t there strictly to make the garment comfortable to wear contributes to the design ease. So, a billowy, gathered, poet’s shirt has lots of design ease. A stretchy yoga top has none (it probably has zero or negative wearing ease, too). A straight skirt made from a woven woolen fabric typically has a couple of inches of wearing ease around the hips. If it were flared from the waist, the first couple of inches would still be considered to be the wearing ease, but that wearing ease would be completely overwhelmed by the design ease, which is why the skirt flares.

The design ease provides the extra fabric that allows the garment to drape, twist, and fold the way it was intended by the designer. So rather than simply provide one-dimensional space around the body, instead it needs to provide two-dimensional, or perhaps even three-dimensional, character to the garment, because it needs to add flare, or what have you.

Exactly how the design ease relates to the body size, though, I can’t rightly say. It isn’t necessarily a direct relationship to size, although that’s probably a decent rule of thumb. For example, say we have a garment for a 34 inch bust that measures 40 inches around, in which the minimum amount of wearing ease is 2 inches. This would mean that there are 4 inches of design ease, which is equivalent to about 12% ease (4 divided by 34). If we used a directly proportional rule, then for a full bust measurement of 48 inches, 12% is 5.8 inches. This means that for a person with a 48 inch bust, the garment should measure 48 + 2 + 5.8 = 55.8 inches. So, the person with the 48 inch bust gets almost 8 inches of total ease, while the person with the 34 inch bust gets 6 inches of total ease.

There could be circumstances where more or less design ease is desirable, according to personal taste.

Taking another hypothetical example, the Big Sack again. It looks a lot better fitting on a model with a 39 inch bust (right) rather than a model with a 33 inch bust (left), because there’s less design ease.

To reprise the history of this sweater, I wanted something big, floopy, and loose, which for me translated to something between 12 and 16 inches of ease. But because of the way the Big Sack is structured (as a raglan sleeve style, and therefore with no specific shoulder “seam” that needs to fit the body), it can fit a range of sizes, with varying design ease, and still look just fine. This probably contributed to the fact that in the SnB book, the sweater was resized in the pattern instructions so that the size pictured in the book was no longer the smaller size. In the case of Banff, if you follow the sizing to arrive at the recommended ease around your own body (12 to 16 inches, which is wearing + design ease), you’ll get the “look” as shown in the photographs. If you don’t follow the guideline of 12 to 16 inches of ease, and go with less, it will still look just fine.

Combining wearing ease and design ease factors
Okay, where does that leave you?

If the amount of total ease (wearing plus design ease) calculated for each pattern size is the same, there’s nothing wrong with that, because many sweater designs can tolerate minor fluctuations in the amount of ease attributed to the design ease. In some circumstances where the garment has a “non-standard” fit (for example, if it’s meant to be tight fitting, or it’s meant to have a great deal of flare or gathering), you may want to reassess whether the size you’re going to knit provides enough, or too much, ease.

Even so, it may not be such an important factor that it requires rewriting the pattern or the dimensions. You might be perfectly content to have a more fitted look — consider the Big Sack pictured above. Just remember that if you simply choose to knit a different size to conform with the amount of ease you want around your bust, you need to make sure that the garment will fit you at the other important fitting points: the shoulders (if the design has set-in sleeves, make sure that the shoulder seam doesn’t wind up being too short or too long), the waist/hip/hem circumference, and of course the length of the body and sleeves.

Percentage systems for calculating sweater dimensions
This explanation of non-proportional wearing ease does not invalidate percentage methods of computing sweater dimensions (for example, the famed EPS system, or anybody else’s numbers for estimating the relative dimensions of a sweater). Percentage systems are premised on the idea that certain proportions of the body are consistent for a given body type, and therefore the analogous measurements of a garment should likewise be proportional. Thus, the typical rule for the yoke depth on a raglan is that it is 25% of the widest body measurement (subject to the addendum that the yoke depth is seldom greater than 10 inches), and so on. Naturally, these percentage systems assume a given body type, so the numbers certainly don’t apply across the board to everyone.

These percentage systems do not necessarily conflict with the statement that wearing ease is non-proportional, because the percentages relate to different measurements. Percentage systems for calculating sweater dimensions start with a chest measurement for the garment; all other numbers for sleeve width, neck width, body length, etc., are based on the initially determined chest measurement. All this discussion about wearing ease has been directed towards finding the appropriate chest measurement in the first place.

But then there’s the question of the amount of ease that should be provided around body parts other than the chest. You might note that the percentage system does imply that the relationship between wearing ease around the torso is proportional to wearing ease around other parts of the body, such as the arm. For example, where the chest measurement of the sweater is assumed to be 100%, the sleeve width of the same sweater is computed to be about 35-40% of the chest measurement. If this is premised on the idea that the actual arm circumference is 35-40% of the full bust measurement, then necessarily the percentage system implies that the amount of ease needed for the arm is reduced by the same amount.

For example, if we assume that a woman with a 32 inch bust has an actual upper arm circumference that is 35% of the full bust measurement, we get 11.2 inches (kind of close, actually a bit larger than the “standard” for that size). Operating on that basis, let’s say we’re working on a sweater with a 34 inch finished bust measurement that is meant to have 2 inches of wearing ease, and no further design ease. It’s in worsted weight yarn, and meant to follow the body’s curves, not skim them (which might require a bit of design ease). Using the percentage system that dictates a sleeve width of 35%, we conclude that the sleeve must be 11.9 inches wide. But that’s less than an inch of wearing ease–is that right?

Possibly. The chest is the part of the body that expands the most during normal body movement; the arms don’t change in dimension so noticeably, unless you’re in the habit of striking bodybuilder poses and have the muscles to back it up. In the course of a survey of about five references on designing knitwear, I found that authors recommended between 50% to 100% of the body ease to be used for the sleeve ease. The general consensus was that the sleeve (unless it had particularly poofy design lines) could not have any more than the body ease if the sleeve were to preserve the same type of fit silhouette as the body. I think that, in the example above, the 0.7 inches of ease might be acceptable provided the sleeve was knit in the round (no sleeve seam), and was in a rather flexible fabric such as stockinette.

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2 Responses to Further ruminations on ease

  1. therisa rogers says:

    This was very helpful, for knitting but more so for sewing. I can figure out better how to plan garment design ease. Thanks again.

  2. amy/knitty says:

    let’s be clear: i don’t cut jenna’s articles cause it’s all good stuff. maybe a smidgen polishing, but that’s all.

    i thank jenna for saving my sanity last issue. getting this extra info in place might have killed me. i should, however, put a direct link to this post in that article. someone remind me.