Bra Size Calculator
Instantly find your perfect bra size from your underbust and bust measurements. Supports 17+ international sizing systems including US, UK, EU, FR, AU, and more. Get sister sizes and size conversions with step-by-step solutions.
Your Measurements
Find Your Perfect Bra Size
Enter your underbust and bust measurements, select your sizing system, and click Calculate to instantly find your perfect bra size.
Complete Bra Size Guide
How to Measure Your Bra Size at Home
Your bra size consists of two parts: the band size (a number) and the cup size (a letter). The band size is your underbust measurement rounded to the nearest even number. The cup size is determined by the difference between your bust and band measurements. Getting accurate measurements is the first step to finding a comfortable, well-fitting bra.
Bra Size = Band Size (number) + Cup Size (letter)
Step-by-Step Measurement Instructions
1. Measure Your Underbust (Ribcage)
Wrap a measuring tape snugly around your ribcage, directly under your bust. Keep the tape level and parallel to the ground. This measurement determines your band size.
2. Measure Your Bust (Fullest Point)
Wrap the tape around the fullest part of your bust, typically at nipple level. Keep the tape level and not too tight. Wear a non-padded bra for the most accurate measurement.
3. Enter Measurements & Calculate
Enter both measurements into the calculator above, select your preferred unit and sizing system, then click Calculate. You'll get your bra size, sister sizes, and sizes in all 17+ international systems.
3 Calculator Modes
Calculate Bra Size
Enter underbust & bust measurements to get your size in all systems with sister sizes.
Size Conversion
Convert any bra size between US, UK, EU, FR, and 13+ other sizing systems.
Sister Sizes
Find alternative sizes with the same cup volume but different band/cup combinations.
Sizing Systems Explained: US vs UK vs EU vs FR
US / CA / MX Sizing
Band sizes 28-50. Cup progression: AA, A, B, C, D, DD, DDD, G, H, I, J, K, L, M, N. Most common in North America.
UK / PK / IN / NZ / AU / ZA Sizing
Same band sizes. Different cup progression after D: DD, E, F, FF, G, GG, H, HH, J, JJ. Widely used in Commonwealth countries.
EU / IT / ES / DE / JP / CN / BR Sizing
Same band sizes as US. Cups: AA, A, B, C, D, E, F, G, H, I, J, K, L, M, N. Alphabetical progression.
FR (France) Sizing
Uses centimeter-based band sizes (add 15 to US/UK band). Cups same as EU. Example: US 34C = FR 49C.
What Are Sister Sizes?
Sister sizes are bra sizes that share the same cup volume but have different band and cup letter combinations. For example, 34C, 32D, and 36B are all sister sizes — they hold the same amount of breast tissue but distribute support differently.
Example: Sister sizes of 34C
Bra Fitting Tips
- Wear a non-padded, well-fitting bra when measuring for the most accurate results.
- Sizes can vary between brands. Always try on when possible, and consider sister sizes.
- The band should be snug and level around your torso. You should be able to fit two fingers under it.
- The center gore (front panel) should sit flat against your chest.
- If you're between sizes, go up a band size and down a cup size (or vice versa) using sister sizes.
Frequently Asked Questions
How do I measure my bra size at home?
Measure your underbust snugly around your ribcage, then measure your bust at the fullest point. Enter both measurements into our calculator to get your size instantly.
What are sister sizes and when should I use them?
Sister sizes have the same cup volume but different band/cup combinations. Use them when your regular size isn't available or when a band feels too tight/loose.
How do US and UK bra sizes differ?
Band sizes are the same, but cup progressions differ after D. US: DD, DDD, G, H. UK: DD, E, F, FF, G, GG. Use our converter for accurate conversions.
Why does my bra size vary between brands?
Different brands use different fit standards and materials. Always try on bras when possible. Sister sizes can help you find a fit in brands that run differently.
Should I measure with or without a bra?
Wear a non-padded, well-fitting bra for the most accurate measurement. The bra should not add extra volume.