Nautilus Swimsuit View A
Sewalongs | Tutorials

How to Choose a Size on a Swimsuit Pattern

To choose the right size for your swimsuit, you’ll have to consider some specific measurements that you would normally not use. It includes total crotch length (also called stride), high hip and high bust measurement. It’s really important to adjust your pattern according to your measurements because a swimsuit is a tight fitting garment that includes your whole torso. Below, I’ll detail these measurements and explain what to consider so that you can best select the size of your swimsuit sewing pattern.

Note: Like any sewing pattern, when sewing a swimsuit you can have a pretty good guess about the right size to start with, but you are well served to make a muslin and use that to fit adjustments specific to your body.

Nautilus Swimsuit View B bottom closeup


A swimsuit is made from 4-way stretch fabric with at least 60-70% stretch, and you want it to fit your body tightly. No flashing when jumping in and out of the water!  Our swimsuits are drafted with 5 inches of negative ease, although you may find you need/want more or less depending on how stretchy your fabric is (not all swimsuit fabrics stretch the same amount) and how snug/supportive you like for your swimsuit to be. This is also why making a muslin is a must for a swimsuit.


Hip is often used for selecting sizes, however this isn’t so helpful when picking a swimsuit size because most swimsuits don’t cover the hip. Instead, we’ve included the high hip measurement. This is taken just under the top bones of your pelvis, the hip bones or Ilia in official terms. This is more accurate than the standard hip measurement, which is taken at the widest part of the hips and may well be much lower, at the top of your thigh bone or femur. Since the swimsuit does not cover this area, taking your high hip measurement gives you a better fitting result.  

Bust Size for Patterns with Cup Sizes: If you are sewing the Nautilus Swimsuit, you need to pick a bust size and a cup size.

The sizes are usually based on your high bust measurements and the difference between full bust and under bust (for the cup size). Make sure that you pay attention to the sizing listed on the pattern and don’t just go by your bra size as sizing can vary.

One thing to note – the size that you get based on your measurements is strongly affected by the shape of your rib cage. Compare your high bust and under bust measurement, and if they differ strongly, pick your size based on your underbust measurement. This could be the case if your rib cage is narrow at the the base for instance.

Analyze your figure

Nautilus Swimsuit View A Jenny
Jenny is wearing a size 26, C/D cup, bottom part lengthened by 2,5″ to adjust for the vertical height of her curves.

Taking a moment to think about where you carry the curves on your body can help you determine how to pick between sizes. Here are some suggestions for some common scenarios:
If you have a round butt: go with your hip size.
If you have a round belly or a flat butt: choose a larger size in the front than in the back.
If you have a broad back: choose a larger size in the back than in the front.

If picking a larger size does not work, consider doing a pattern adjustment like a full tummy adjustment. We will post a tutorial on how to do this soon.

Again, these are all suggestions for choosing the right size to start. You may need to sew a muslin of your swimsuit to perfect the sizing and fit for your unique body.

Similar Posts


    1. Ooh, that’s a sexy swimsuit!
      I’m afraid that the way the Nautilus Swimsuit is constructed would make it non-trivial to turn it into your inspiration suit. For that suit, the fronts don’t have a seam under the bust. The Nautilus has a seam under the bust that is necessary for the twist construction but would look odd if it was lowered in order to lower the decollete.
      If you wanted to make the Nautilus Swimsuit just a bit sexier, you could shave off some of the fabric from the top of the cup. I would recommend doing this after you have made most of the suit but before you attach elastic to the top of the suit cups (you will need to shuffle the construction order a bit to do this).
      Hope this helps!

  1. I’m doing research on how to do swimsuits, planning to put up my own swimsuit line. This is very helpful. Thank you for posting. :)

Leave a Reply

Your email address will not be published. Required fields are marked *