Free Tool
Bra Size Calculator
Enter two measurements. Get your size, sister sizes, and a fit tip — in seconds.
Your estimated size
—
This is a fit estimate based on standard sizing formulas. Sizing varies by brand — always try a style on before buying. Not medical advice.
How to measure your bra size at home
Accurate results start with an accurate measurement. Use a flexible fabric measuring tape — a rigid tape won’t sit correctly against the body.
- Measure your band. Wrap the tape snugly around your ribcage, directly under your bust, keeping it level all the way around. Breathe normally.
- Measure your bust. Wrap the tape around the fullest part of your bust, level with the floor and relaxed, not pulled tight.
- Enter both numbers into the calculator above and choose inches or centimeters.
- Read your result. Your size, two sister sizes, and a fit tip appear instantly.
Understanding sister sizes
A sister size has the same cup volume as your main size, just split across a different band-and-cup combination. Sizing up the band always pairs with sizing down the cup letter, and vice versa. They’re useful when your usual size is out of stock, or when a brand’s fit runs differently than you expect.
Frequently asked questions
How accurate is this bra size calculator?
It uses the standard band-and-bust formula most fitting guides rely on. It’s a strong starting estimate, but fit still varies by brand, so trying a bra on is the best final check.
What if my measurement falls between two sizes?
Round to the nearest whole number before entering it. If you’re exactly between two band sizes, try the smaller band first, since bands stretch slightly with wear.
What is a sister size and why does it matter?
A sister size has the same cup volume as your main size but a different band-and-cup combination. It’s useful when your usual size is out of stock or a brand runs differently.
Do I need a tape measure to use this calculator?
Yes, a flexible fabric measuring tape gives the most accurate result. A rigid tape measure won’t sit correctly against the body.