Health and Fitness / Free Tools
Free Bra Size Calculator
Use this free bra size calculator to find your band and cup size from two simple measurements. Enter your band and bust measurements and see your size in US, UK, and EU sizing at once - no sign-up required.
What is a bra size calculator and why it matters
A bra size calculator converts two simple body measurements - band (underbust) and bust - into a band and cup size using a standard sizing formula. This matters because bra sizing is not something most people check often, and body measurements can shift over time due to weight changes, so a size bought years ago may no longer be accurate. Getting the band and cup size right affects both comfort and support, and this calculator gives a solid starting point before trying sizes on.
How this calculator works
The band size is calculated by rounding your underbust measurement to the nearest whole number and adding a standard sizing adjustment, following the same method used in most bra fitting guides. The cup size is then based on the difference between your bust measurement and that calculated band size - each inch of difference corresponds to one cup letter. UK and EU sizing use the same underlying measurements but different letter and number conventions, which this calculator converts automatically.
Common searches this calculator answers
- How do I calculate my bra size from measurements?
- What is my band size and cup size?
- How do I convert my US bra size to UK or EU sizing?
- How do I measure myself correctly for a bra size?
- What does a sister size mean in bra fitting?
How to measure yourself
- Wear a non-padded, well-fitting bra (or no bra) for the most accurate measurement.
- Band: wrap a soft tape measure directly under your bust, snug but not tight, keeping it level all the way around.
- Bust: wrap the tape around the fullest part of your bust, keeping the tape level and not pulled tight.
- Enter both measurements above in inches or centimeters and click Calculate my size.
Cup size reference (by measurement difference)
| Difference | US cup | UK / EU cup |
|---|---|---|
| 0" | AA | AA |
| 1" | A | A |
| 2" | B | B |
| 3" | C | C |
| 4" | D | D |
| 5" | DD / E | DD |
| 6" | DDD / F | E |
| 7" | G | F |
| 8" | H | FF |
| 9" | I | G |
Tips
- If your calculated size feels off, try a "sister size" - the same cup volume in a different band: one band size up with one cup size down, or one band size down with one cup size up.
- Re-measure every year or two, or after any significant weight change, pregnancy, or surgery, since band and cup size can shift independently of each other.
- A band that rides up in the back is usually too loose; a band that digs in or leaves deep marks is usually too tight - the band should sit level and feel snug but comfortable.
- Sizing runs differently between brands, especially between everyday and specialty or sports bras - treat a calculated size as your starting point when trying a new brand, not a guarantee.
Frequently asked questions
Is this bra size calculator free to use?
Yes. It is completely free, works in your browser, and does not require any sign-up or download.
Why is my calculated size different from what I currently wear?
Bodies change over time, and many people end up wearing an incorrect size without realizing it, often due to measuring over a padded bra or an outdated measurement. If your current bra was properly fitted recently, trust that fit - otherwise this calculator may be more accurate than what you're currently wearing.
What is a sister size?
A sister size is a different band and cup combination that has approximately the same cup volume as your calculated size - for example, a 34C and a 36B have very similar cup volume. Sister sizes are useful when a specific brand's exact size doesn't fit well.
Does this calculator work for all cup sizes?
It covers the standard range used by most sizing charts. Very large or very small differences between band and bust measurements may fall outside typical retail size ranges, in which case a specialty or made-to-measure retailer may offer a better fit.
Why do UK and US cup letters differ at larger sizes?
US and UK sizing use the same measurement method but different letter naming conventions starting around a DD/E cup, which is why this calculator converts between the two rather than assuming the letters match directly.
