Bra Size Calculator
Find your perfect bra size with our free Bra Size Calculator. Enter your underbust and bust measurements to determine your band size, cup size, and US, UK, and EU sizing. Get a comfortable and supportive fit every time.
What Is Bra Size?
Bra size is a combination of two measurements: the band size (the number, e.g., 34, 36, 38) and the cup size (the letter, e.g., A, B, C, D). The band size represents the circumference of your ribcage just under your breasts, while the cup size represents the difference between your bust measurement and your band measurement.
Cup size is relative to band size — a 34C has the same cup volume as a 36B or a 32D. This is why finding the right combination is essential for comfort and support.
How Does the Bra Size Calculator Work?
The calculator uses the following steps to determine your bra size:
Step 1: Band Size
Round your underbust measurement to the nearest whole number. If it's an even number, that's your band size. If it's odd, add 1 to get an even band size.
Step 2: Cup Size
Subtract your band size from your bust measurement. Each inch of difference equals one cup size:
1" = A, 2" = B, 3" = C, 4" = D, 5" = DD/E, 6" = DDD/F, and so on.
Step 3: Your Bra Size
Combine your band size and cup size. For example: 34B, 36C, 38DD.
The calculator supports US, UK, and EU sizing systems and can show sister sizes — alternative sizes with the same cup volume that may fit better in different brands.
Why Use This Bra Size Calculator?
- Accurate Sizing: Uses the standard formula for band and cup size calculation.
- Multiple Systems: Supports US, UK, and EU sizing.
- Sister Sizes: Find alternative sizes that may fit better in different brands.
- Visual Breakdown: A chart shows your measurements and how they translate to size.
- Free & Private: No registration, no data storage.
Understanding Bra Size Systems
- US / Canada: Uses band sizes 28-52 and cup sizes A, B, C, D, DD, DDD, G, H, I, J, K.
- UK / Australia: Uses band sizes 28-52 and cup sizes A, B, C, D, DD, E, F, FF, G, GG, H, HH, J.
- EU / International: Uses band sizes 60-130 (in cm) and cup sizes A, B, C, D, E, F, G, H.
❓ Bra Size Calculator FAQ
How do I measure my bra size at home?
Wear an unpadded bra and use a soft tape measure. Measure your underbust firmly around your ribcage just below your breasts. Then measure your bust loosely around the fullest part. Enter both measurements into the calculator for your size.
What is the difference between band size and cup size?
Band size is the measurement around your ribcage under your breasts (e.g., 34, 36, 38). Cup size is the difference between your bust measurement and band size, expressed as a letter (A, B, C, D, etc.).
How is cup size calculated?
Subtract your band size from your bust measurement. Each inch of difference equals one cup size: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD/E, 6" = DDD/F.
What is the difference between US and UK bra sizes?
US and UK band sizes are the same (34, 36, 38, etc.). Cup sizes differ from DD upward. US uses DDD, G, H, I, J, while UK uses E, F, FF, G, GG, H, HH, J.
What are sister sizes?
Sister sizes are alternative sizes with the same cup volume. For example, 34C, 36B, and 32D all have the same cup volume. If a band size doesn't fit perfectly, trying a sister size may help.
How do I know if my bra fits correctly?
A well-fitting bra has the band sitting horizontally around your torso, the center gore flat against your chest, no spillage or gaping in the cups, and the straps staying in place without digging in.
What is the average bra size?
The average bra size varies by region. In the US, the average is around 34DD, while in the UK it's around 36D. However, bra sizes vary widely and what matters most is finding the right fit for your body.
How often should I measure my bra size?
You should measure your bra size every 6-12 months or whenever you notice changes in your body weight, pregnancy, or menopause. Your bra size can change over time due to various factors.
What is the difference between a 34B and a 36A?
34B and 36A are sister sizes — they have the same cup volume. The 34B has a smaller band (34") with a larger cup, while the 36A has a larger band (36") with a smaller cup.
Why does my bra size vary between brands?
Different brands use different sizing standards and manufacturing techniques. This is why sister sizes are useful — a 34C in one brand might fit like a 36B in another.
What is the underbust measurement?
The underbust measurement is the circumference of your ribcage just below your breasts. It determines your band size. Measure firmly with a soft tape measure.
What is the bust measurement?
The bust measurement is the circumference around the fullest part of your breasts. It is used together with the underbust measurement to determine your cup size.
What if my underbust measurement is an odd number?
If your underbust measurement is odd, round up to the next even number. For example, 33" becomes 34". This ensures the band sits comfortably and securely.
What is the difference between UK and EU bra sizes?
UK and EU use different band size numbering. A UK 34 band is approximately an EU 75 band. Cup sizes also differ — a UK D is roughly an EU E. This calculator handles both systems.
How do I convert my bra size to a different system?
Use the sizing system selector in the calculator to view your size in US, UK, or EU sizing. The conversion accounts for differences in band and cup labeling between regions.
What should I do if I'm between cup sizes?
If you're between cup sizes, try the larger cup size first. You can also try sister sizes. For example, if you're between a C and a D, try both and choose the one that fits more comfortably.
How does pregnancy affect bra size?
Pregnancy can cause significant changes in breast size due to hormonal changes. Many women need to go up several cup sizes during pregnancy and breastfeeding. Re-measure regularly for comfort and support.
What is the best bra for my body type?
The best bra depends on your body type and needs. Full-coverage bras offer more support, balconette bras create lift, and sports bras provide support during exercise. This calculator helps you find your size so you can choose the right style.
Is this bra size calculator accurate?
This calculator provides a reliable estimate based on standard bra sizing formulas. However, different brands may fit differently, and personal comfort is the most important factor. Try on bras to confirm the best fit for you.
What is the difference between a push-up bra and a regular bra?
A push-up bra has padding at the bottom of the cups to lift and push the breasts together, creating more cleavage. Regular bras provide support without additional padding. This calculator helps you find your size for any style.