Bra Size Calculator

How bra size is calculated

Your band size comes from your underbust measurement rounded to the nearest whole number, plus 4 inches if that number is even or 5 inches if it's odd. Your cup size is based on the difference between your bust and band measurements each inch of difference is one cup size, from AA up through the alphabet.

How to measure yourself for a bra

Wearing a well-fitting, non-padded bra, wrap a soft tape measure snugly around your ribcage directly under your bust for the underbust measurement, and around the fullest part of your bust for the bust measurement. Keep the tape level and parallel to the floor for both.

Understanding Cup Sizes

Cup size increases with each inch of difference between your bust and band measurements. An A cup is a 1-inch difference, B is 2 inches, C is 3 inches, and so on through the alphabet. Some specialty retailers offer extended sizes beyond what this calculator shows, and international sizing systems use different measurements entirely, so your US size may not directly convert. If you're also looking to find your ring size, we have a similar calculator for that as well using hand measurements.

Why Accurate Measurement Matters

A properly fitting bra improves comfort, posture, and the look of your clothes. Many people wear the wrong size because they measure incorrectly or don't account for how sizes vary by brand. Taking time to measure carefully with a soft tape measure (not a hard ruler) and trying on multiple sizes ensures you find what works best for your body.

Common Measurement Mistakes

The most common errors include pulling the tape measure too tightly, measuring over clothing instead of directly on skin, and not keeping the tape level and parallel to the floor. These mistakes can throw off your size by a full cup or band, so remeasure if your size doesn't feel right when you try it on.

FAQ

What if my band and bust measurement are the same?
A zero-inch difference means an AA cup the smallest standard cup size.

Do bra sizes vary between brands?
Yes this calculator gives you a standard US size to start from, but fit varies by brand and style, so it's still worth trying a size on when possible.

Should I measure over or under my clothes?
Always measure directly against your skin wearing no bra or a non-padded bra, as this gives the most accurate measurements for proper fit.

What if my measurements fall between sizes?
Round to the nearest whole number for your band size. If you're between cup sizes, try both and choose the one that feels most comfortable.

Is this calculator accurate for all body types?
This calculator uses the standard US sizing method. Individual fit depends on breast shape, density, and brand design, so trying on in person is always recommended.