The principles of fitting and grading any swimsuit are pretty similar, so no matter what pattern you are using, you’ll hopefully find some helpful information to fit and grade any swimsuit sewing pattern amongst the specific example of the Nautilus Swimsuit. Before you start any fitting and grading, make sure you are starting with the best base size by reading How to Choose a Swimsuit Pattern Size.
Cup Size: The Nautilus Swimsuit pattern has 4 different cup size options ranging from AA to DD+. Measure the difference between your full bust and your under bust to get your suggested size. 0-1″ = AA, 1-3″ = A/B, 3-5″ = C/D, and >5″ = DD+. However, this is just a starting point (like any other sizing) and you will want to make a muslin to determine that you are getting a proper fit.
What might cause the wrong fit? The cups on the Nautilus Swimsuit are generously sized so if you are between sizes, your best bet is to size down. Additionally, the shape of your rib cage and the fullness of your breasts can greatly affect the size you should choose. For example, The difference between my under bust and full bust is 3+” however I most definitely do NOT fit the C/D and I could actually wear the AA if I chose. The reason is that my rib cage is narrow at the bottom and wider at the top so much of the difference between under bust and full bust is caused by changes in the size of my rib cage and not actually from breast tissue. If this rings true to you too, round down a size.
What might the wrong fit look like? If the bottom of your cup is significantly below the bottom of your breast, the cup size is too large. If the bottom of your cup doesn’t go below the bottom of your breast, the cup size is too small.
How do you fix the wrong fit? In the Nautilus Swimsuit, it’s as simple as picking a different pattern piece. For a swimsuit pattern that doesn’t include separate cup size options, you can apply the principles of an FBA or SBA to your swimsuit.
Band/Body Size: Band size should be chosen independently of your bust size. This is easy in the Nautilus Swimsuit pattern since both are separately graded pieces. However, you should keep this fact in mind when sewing a pattern that doesn’t grade them separately and consider that you may need to add/subtract width independent of bust fullness which may require reshaping of pattern pieces. For the Nautilus Swimsuit, the cup size determines the vertical fit of the cup while the band size determines the horizontal fit of the cup (as well as the size across the back). Remember that you can choose separate sizes for the front and back of your body to get the best possible fit.
What might cause the wrong fit? The wrong cup size may make it look like you have the wrong band size, so first make sure that your cup is fitting correctly. The shape of your rib cage can affect fit as well as where the curves are on your body. For example, if you have a round belly, you may need to go up a size in the front and if you have a broad back you may need to go up a size in the back.
What might the wrong fit look like? If the swimsuit feels, well, too small, you probably need to go up a size all around. If it pulls away from your body too easily when you move around in it, you probably need to go down a size. The positioning of the side seam can give you information about fitting specifically the front or back of your body – the side seam should be in the center of your side.
How do you fix the wrong fit? Go up or down a size. It’s that easy. Remember that you may need a different size for your front than back depending upon how your own body is shaped.
Length: The Nautilus Swimsuit pattern tells you what torso length it was intended for each size, but not all patterns do. You can guess that a pattern is designed for an “average” torso length, unless it tells you otherwise. So, if you already know that you have a long or short torso and usually make an adjustment to torso length on other sewing projects, then know you should make the same adjustment on your swimsuit. (Note: Length information is all for one piece suits. For a two piece you don’t need to worry!).
What might cause the wrong fit?You may find that your needs differ from the suggested length because of differences in the shape of your body or the stretch of your fabric. If your fabric doesn’t stretch well in both directions (see information on Selecting Swimsuit Fabric), the direction of worse stretch will be the vertical direction and if this is the case, you might need to lengthen your pattern. Additionally, since swimsuits have 4 way stretch and are worn with significant negative ease, the size you choose and how it stretches around your body can affect your length – if the fabric is being taken up by stretching around a particularly curvy part of your body there will be less stretch left to cover you vertically so this can cause you to need to increase your torso length (or on the flip side if you find that your torso length is too short, you may be able to fix it by going up a size).
What might the wrong fit look like? A wedgie. If your suit is pulling into you uncomfortably or if the curve of the suit is higher on your front hip or on your cheek than it should be then the torso length is probably too short. On the flip side, if your suit feels droopy or loose or has extra fabric wrinkles, then the length is probably too long. If you are totally sure that your cup size is chosen correctly, then a too-short suit can also show itself by how it pull down on the seam between top and bottom. (You can see that the swimsuit I’m modeling in the release photos is actually a bit too short in the torso for me (I totally forgot to make any of my standard fit adjustments when I sewed the final pattern. Derp!) because it’s a bit cheekier than intended).
How do you fix the wrong fit? Slash your pattern at the “lengthen/shorten here” line and add an inch or two. Then smooth the line at the side of the suit. If your swimsuit doesn’t have a lengthen/shorten line then you can add one yourself. This line can be between the natural waist and crotch or between the natural waist and bust (or distributed over both). This is where knowing your body can be helpful. (For example, I know that my torso is a bit longer than average but all of that extra length is between my true waist and crotch. I’m actually a bit short waisted between bust and true waist, despite being 5’10”.) As a general rule, I’d suggest erring a bit on the long side over a bit on the short side since nothing is worse than a wedgie.