Ease and the Internal Measurement

Courtesy of Kurt M. Fowler

Internal measurement of a knitted fabric can differ quite dramatically than the outside finished measurement. The internal measurement affects the amount of ease in a knitted garment .For those of you new to the concept that knitted fabric has a separate internal measurement, Kurt M. Fowler took the time to describe the mathematics for us.

We are looking down on a sweater from a balcony up above, and we are imagining a horizontal slice through the center of the body. The circle we see is not a thin line. It is as thick as the knitted fabric, and even in thin stockinette, the fabric is about twice as

thick as the yarn. Picture the outside surface as one thin-line circle and the inside surface as another thin-line circle within the other circle.

Say the diameter of your outside surface circle is 14 inches (about what a sweater with a 44-inch chest would be). Let's say the fabric is an eighth of an inch thick. Pretty thin, right? Shouldn't affect the inside all that much, right? Wrong. The diameter of your inside circle is a quarter of an inch shorter (subtracting two thicknesses of fabric, front and back). The inside-surface diameter is then 13.75 -- and now we get to the fun part.

Circumference = pi (3.1415926535897932384626433832795) times diameter.

Perhaps you'd prefer to use 3.14 for pi to simplify matters.

So in the example above, the circumference of the outside surface of the sweater is pi times 14, or 43.98 inches.

The circumference of the inside surface of this sweater is pi times 13.75, or 43.19 inches -- almost an inch less room -- and that's with a thin yarn and thin fabric.

What if the fabric is thick (e.g., bulky yarn, cables, and/or garter stitch, etc.), and the inside-surface diameter is .75" less than the outside? (Two thicknesses of Aran texture could easily add up to .75”, right?) Still doesn't seem like less than an inch would matter much. However...

13.25 times pi = 41.63 -- compared to the 44-inch outside surface, a difference of 2.37 inches on the inside!

I hope these examples help. (geometry is not my best subject, so don't be shy about pointing out errors if I have any)

Kurt