Bra Size Calculator
Find your estimated bra size using your bust and underbust measurements.
Enter Your Measurements
Advanced mode uses three underbust and three bust measurements for a more refined estimate. Measuring guide.
Choose Your Country
Bra cup letters differ by country once you go past DD. Pick the calculator that matches the brands you shop.
How to Measure Your Bra Size
You only need a soft measuring tape and a couple of minutes. Read the full step-by-step measuring guide for details.
Measure your underbust. Wrap the tape directly under your bust where the band sits, keeping it level and snug.
Measure your bust. Wrap the tape around the fullest part of your bust, level across your back, without pressing in.
Enter your numbers. Type both measurements into the calculator above, choosing inches or centimeters and your sizing system.
Check your result. Use the estimated size as a starting point — then try on and adjust, since brands vary.
Bra Size Chart and Sister Sizes
The bra size chart shows how band and cup sizes map across US, UK, and EU sizing, so you can convert between systems at a glance.
Need a different band with the same cup volume? Try our sister size calculator — for example, the sister sizes of 34C are 32D and 36B, handy when your usual size is out of stock or the band feels slightly off.
From the Blog
Frequently Asked Questions
How does the bra size calculator work?
You enter two measurements — your underbust (just under your bust) and your bust (around the fullest part) — in inches or centimeters. The calculator converts centimeters to inches, rounds your underbust to the nearest even inch for the band size, and sets the cup size from the difference between your bust and band measurements. Advanced mode refines this using three underbust and three bust measurements.
How do I measure my underbust?
Wrap a soft measuring tape directly underneath your bust, where the bra band sits. Keep the tape level all the way around and snug but not tight, then breathe out normally and read the measurement. This is the most important measurement for your band size.
How do I measure my bust?
Wrap the tape around the fullest part of your bust, usually across the nipples. Keep the tape level across your back and snug enough to stay in place without pressing in. Stand upright and breathe normally while you read it.
Should I wear a bra while measuring?
It is best to measure without a bra or in a thin, unpadded bra. A padded or push-up bra lifts and compresses the bust, which can give a smaller or distorted bust measurement and an inaccurate result.
Why does my bra size vary between brands?
Bra sizing is not fully standardized, so a 34C from one brand can fit differently from a 34C from another. Bands may run snug or loose, cups may run shallow or deep, and sizing steps differ by country. Always treat a calculated size as a starting point and check each brand's size chart.
What are sister sizes?
Sister sizes are bra sizes with roughly the same cup volume but different band sizes. For example, the sister sizes of 34C are 32D (one band down, one cup up) and 36B (one band up, one cup down). They are useful when your usual size is out of stock or the band feels too tight or too loose.
Can my bra size change over time?
Yes. Weight changes, pregnancy, breastfeeding, hormonal changes, and aging can all change your bust and underbust measurements. It is worth re-measuring every year or two, or whenever your current bras stop fitting comfortably.
Are US and UK bra sizes the same?
Band sizes use the same numbers in both systems, but cup letters differ once you go past DD. For example, a US DDD is labeled E in UK sizing, and a US G is labeled F in UK sizing. Use the Country selector in the calculator to get the right letters for your region.
How accurate is this calculator?
The calculator gives an estimate based on standard sizing math, and it cannot guarantee a perfect fit — no online calculator can. Bodies and bra styles vary too much for any formula to be exact every time. Use your result as a starting point, then try on bras and adjust from there.