Are you wearing the right swimwear cup size?
Finding the perfect swimsuit can feel like a challenge—especially if you’re also struggling to find the right bra cup size. Many women wear the wrong cup without even realizing it, which often leads to swimsuits that don’t feel as comfortable or supportive as they should.
While it may seem complicated, finding your ideal fit is actually simpler than you think. With a few easy measurements and a better understanding of your body, you can discover swimwear that truly fits and flatters.
In this guide, we’ll show you how to measure correctly and how to choose the right swimwear for your cup size—so you can feel confident and comfortable every time you wear it.
Before we begin, we recommend revisiting your measurements at least once a year to ensure you’re still wearing your best fit. Since our bodies naturally change over time, taking a moment to double-check before choosing new swimwear can make all the difference.
To get started, you’ll need a soft measuring tape and a mirror. Make sure to write down your measurements, and repeat each one 2–3 times to ensure you’re getting consistent and accurate results.
To find your correct bra cup and band size, you’ll need two measurements: underbust and overbust. When measuring, stand in front of a mirror with your back straight. It’s important to remain standing upright, as this helps ensure your measurements are as accurate as possible.
Measuring your underbust
Place the measuring tape directly under your bust and wrap it snugly around your body. It should feel firm, but not so tight that it digs into your skin. Make sure the tape runs straight across your back and stays parallel to the floor, sitting evenly from end to end.
Once you have your measurement, write it down and repeat the process one more time to ensure accuracy.
If your measurement is an odd number, we recommend rounding it up to the nearest even number. Band sizes usually range from 65 to 110 and increase in increments of 5.
In the table below, you can find how your measurement translates into your correct band size.
| Underbust size | 65 | 70 | 75 | 85 | 90 | 95 | 100 | 105 | 110 |
| Underbust measurment | 63-67 cm | 68-72 cm | 73-77 cm | 83-87 cm | 88-92 cm | 93-97 cm | 98-102 cm | 103-107 cm | 108-112 cm |
For example, if your measurement is 83.6 cm, you would round it up to 84 cm, which corresponds to a band size 85.
It’s important to note down your exact measurement, as you’ll need it for the next step.
Measuring your overbust (standing bust)
To measure your overbust, place the measuring tape around the fullest part of your bust—typically across the nipple line. Make sure the tape sits straight across your back and remains parallel to the floor.
It should rest comfortably on your body without being too tight—avoid pulling it so tight that it presses your breasts together, digs into your skin, or pinches.
Once you have your measurement, write it down and repeat the process one more time to ensure accuracy.
Determining your bra cup
After taking all your measurements, you can calculate your cup size using a simple formula: subtract your underbust measurement from your overbust measurement.
The difference between these two measurements will determine your cup size, as shown in the table below.
| Cup Size | A | B | C | D | E | F |
| Overbust - Underbust | 12 cm | 14 cm | 16 cm | 18 cm | 20 cm | 22 cm |
For example, let’s say your overbust measurement is 99 cm and your underbust measurement is 85 cm. The difference between them is 14 cm.
According to the table above, this corresponds to a B cup, meaning your bra size would be 85B.
To make things even easier, we’ve provided a detailed table below to help you find your perfect size—no calculations required.
| Underbust (cm) | Overbust (cm) | Cup size | Bra size |
|---|---|---|---|
| 65-70 | 77-82 79-84 81-86 83-88 |
A B C D |
65A 65B 65C 65D |
| 70-75 | 82-87 84-89 86-91 88-93 |
A B C D |
70A 70B 70C 70D |
| 75-80 | 87-92 89-94 91-96 93-98 |
A B C D |
75A 75B 75C 75D |
| 80-85 | 92-97 94-99 96-101 98-103 |
A B C D |
80A 80B 80C 80D |
| 85-90 | 97-102 99-104 99-106 103-108 |
A B C D |
85A 85B 85C 85D |
Now that you’ve found your ideal size, it’s important to remember that swimwear fit can vary depending on the style, fabric, and level of support.
That’s where sister sizes come in—they give you more flexibility and help you find your best fit, even when your exact size isn’t available.
How to find your sister size?
Sister sizes are alternative sizes that have the same cup volume but a different band size. When you go down in band size, you need to go up in cup size to keep the same cup volume. And when you go up in band size, you go down in cup size.
For example:
If your usual size is 85B:
- Going down a band -80C
- Going up a band -90A
Even though the numbers and letters change, the cup volume remains very similar.
This can be especially helpful when:
- your usual size feels slightly too tight or too loose
- a specific swimsuit style fits differently
- your exact size isn’t available
Sister sizes give you flexibility, allowing you to find a better fit without compromising on support or comfort.
As a general rule:
- If the band feels too tight, try going up a band and down a cup
- If the band feels too loose, try going down a band and up a cup
Understanding sister sizes makes it much easier to find swimwear that truly fits your body—so you can feel confident, supported, and comfortable in every piece you wear.
Finding your perfect fit doesn’t have to be complicated. With the right measurements and a better understanding of how sizing works, you can choose swimwear that truly supports your shape and feels comfortable to wear.
Because the right fit is more than just numbers—it’s what allows you to feel confident, secure, and completely at ease in your swimsuit.
At Noire Swimwear, we’re always working to improve the way our pieces fit, including expanding our range of cup sizes to better suit different body types.
Discover more about our extended cup size range here: A Better Fit for Every Body: Discover Our Extended Size Range