How to Choose a Size on a Swimsuit Pattern


When I’m sewing a pattern that I haven’t sewn before, I usually jump straight to the pattern pieces and measure the high bust and the hip to choose what size I will sew. Patterns often don’t list their finished measurements and sizing charts often don’t say how much ease they include but a pattern piece reveals all. However, this technique falls apart when selecting a swimsuit size for many reasons. Below, I’ll detail these reasons and explain what to consider instead 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

Ease: For fitted garments with stretch, 0-2 inches of negative ease gives a pretty reliable modern fit and for fitted garments without stretch, 1-2 inches of positive ease does the same. However, these ballpark figures are NOT helpful when picking out a swimsuit size because you want MANY inches of negative ease in your swimsuit. A ballpark number to start with is 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.

Nautilus Swimsuit View B top back

Measurements: High bust and hip are often used for selecting sizes however they aren’t so helpful when picking a swimsuit size because most swimsuits don’t cover the high bust or the hip so you can’t get an accurate measurement for that area off of the pattern pieces. Instead, try measuring your high hip and your under bust and comparing those measurements to the pattern pieces.


Bust Size: This may seem obvious, but if you typically need to do an FBA or SBA on your patterns, for most swimsuit patterns you will probably need to do one as well. If your FBA or SBA adjustments aren’t more than an inch (maybe 2), then you might be able to get away with just choosing a size larger for the top.

Bust Size for Patterns with Cup Sizes: If you are sewing the Nautilus Swimsuit, another swimsuit that has cup sizes independent of band sizes, or if you are converting a bra pattern to a swimsuit top, you need to pick a bust size and a cup size. The sizes are usually based on your under bust measurements (for the band size) 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. If you know that your rib cage is narrow at the the base, if your size based on your under bust measurements is multiple sizes away from your size based on your waist measurements, or if you know that the difference between your under bust and full bust measures to be larger than the cup size you normally wear – go up a size or two in the band size.

Nautilus - Swimsuit-Thumbnail

Analyze Your Figure: 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 the full part of your hips is low: go with your waist size.
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.

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.


Comments 5

  1. Heey!!

    You’ve created an awesome swimsuit pattern!
    I was wondering if I can make the v-neckline deeper as a modification.
    I was eyeing this swimsuit (http://www.asos.com/pistol-panties/pistol-panties-joss-teal-animal-swimsuit/prod/pgeproduct.aspx?iid=4239232&clr=Teal&SearchQuery=pistol+panties&pgesize=36&pge=1&totalstyles=58&gridsize=3&gridrow=1&gridcolumn=1&utm_source=Affiliate&utm_medium=LinkShare&utm_content=UKNetwork.1&utm_campaign=QFGLnEolOWg&cvosrc=Affiliate.LinkShare.QFGLnEolOWg&link=15&promo=273171&source=linkshare&MID=35718&affid=2134&WT.tsrc=Affiliate&siteID=QFGLnEolOWg-ZpUVhhBkabmZDslt1OfuHA&un_jtt_redirect) so long and I thought why not make it myself.
    So I thought if I could make this decolleté deepr, it would be awesome.
    Do you have any advice?

    1. Post

      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!

  2. 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. :)

  3. Is there any general guideline for the amount of negative VERTICAL ease in a 1 piece. I understand the negative ease associated with the usual horizontal measurements but I usually have a problem in the amount of length in a 1 piece suit. So, if the total torso measurement is 60″ (going all the way around the body through the crotch and to the same shoulder), is there a guideline for the amount of negative ease that will allow for a snug fit but not too small? I’m thinking something like 3″ so the total finished suit measurement would be 57″. Or do you just sew the length of the torso? I’m thinking of using 4 way stretch fabric that’s got 50% stretch. Hopefully this makes sense…

    1. Post

      That’s a good question, and a little tricky to answer. The more negative horizontal ease you have, the more vertical ease you’ll need as stretching a fabric one way contracts it the other. Also, it will depend a lot on the amount of stretch in your fabric and lining – the stretchier the fabric the more ease you can handle. Modern fabrics are usually a lot more stretchy, particularly in the vertical direction, than older fabrics. Also, it’s definitely better to have a bit too much vertical ease than a bit too little!

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