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.
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.
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.
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.