How to Choose a size with Negative Ease

How to Choose a size with Negative Ease

But what about choosing the proper size for a knit garment? It's so confusing with terms like negative ease, and a range of stretch percentages a garment can be sewn from. Aside from just winging it, there is a way to determine whether a pattern will comfortable fit you prior to cutting it all out and sewing it: math.

If you aren't like me and a total nerd for math, you might have let out an audible groan. I totally get it! Math can be quite a literal headache. But there is also something magical about knowing that math never lies (unless you make a mistake or your calculator is a jerk for the day). '

Let's take my fabric as an example and the size chart for the Nathalie Bodysuit.

My body measurements are as follows:

  • Bust: 37”
  • Waist: 28 1/2”
  • High Hip (Since the pattern doesn't include finished hip measurements): 36”
  • Front Rise (From waist to crotch): 14”

I'll put those measurements to the back of my mind for now as I dive into the math!

Based on my measurements, I would be a size C in the Nathalie. The finished garment measurements for size C for those same areas are:

  • Bust: 28”
  • Waist: 23 1/2”
  • High Hip: 32”
  • Front Rise (From waist to crotch): 12 1/16”

As you can see, those measurements are WAY smaller than my actual measurements! To determine if this will fit me comfortable I am going to use the following formula for the Bust, Waist & Hips:

{Size C Measurement X 0.3 (i.e. 30%) } + Size C Measurement = Total amount Garment will comfortably stretch

I will then use the following formula for the Front Rise of my garment. It's the same but I have swapped out the 30% stretch with 20% stretch because I have less vertical stretch in my fabric:

{Size C Measurement X 0.2 (i.e. 20%) } + Size C Measurement = Total amount Garment will comfortably stretch

Here are the new measurements based on the above calculations for my particular fabric:

  • Bust: 36.4”
  • Waist: 30.55”
  • Hips: 41.6”
  • Front Rise (From waist to crotch): 14.475”

As you can see, if I were to compare these new numbers to my actual body measurements, I am would be pretty close to fitting comfortably with this particular fabric in this particular size. The only exception might be my bust- it would more than likely be stretching the fabric quite snugly across my chest, or flattening my bust every time I wear the bodysuit, so I would plan to size up in that area! I might even add a bit of extra length to the rise because having less than 1/2” of extra stretch sounds like a recipe for a wedgie.

If you want to go an even simpler route, you can use the following formula, which comes courtesy of Arlen. We were chatting over street tacos and he spouted off this brilliance:

{Finished Garment Measurement of Pattern x 1.(whatever your fabric stretch percentage is)} = Total amount Garment will comfortably stretch

By adding the 1.(x) in front of your percentage, you are effectively adding in 100% of the finished garment measurement at the same time you are calculating how much it will additionally stretch. Using my fabric as an example for the Bust I would do the following:

28” x 1.2 = 33.6”

Which is the same answer I got from the first formula, I just got it faster!

Back to blog


Hi. That 33.6" you got using Arlen’s formula is not the same bust measurement you got using the first showed formula. With the longer formula you got, 36.4" So did you make a mistake in using wrong stretch percentage in Arlen’s formula. As you started with .3 in the first and used .2 in Arlen’s. You had only used .2 for the front rise due to less vertical stretch.


The new meas are not making sense applying 30% stretch from bust to waist to hips. The Bust is .6" smaller that the body meas (37" to 36.4") while the waist and hips are 2-5.5" bigger (28.5" to 30.6" waist and 36" to 41.6" hips).


Hi administrator, You always provide practical solutions and recommendations.

Aracely Stansbury

Yay! That makes me so happy to hear, Carmen!

Brittani Bumb

Brilliant!! Using this to figure out a swimsuit size. Thank you!

Carmen Salomé

Leave a comment