Bra Size Calculator
This bra size calculator turns two simple measurements — your underbust (band) and bust (full) — into your size across six international standards: US, UK, EU, FR, AU/NZ, and JP. Enter your numbers and see your band and cup instantly.
It is built for anyone shopping online from international brands, confirming a current size, or measuring at home for the first time. Alongside your main size, the calculator suggests sister sizes — alternatives with the same cup volume but a different band — so you have options when your exact size is out of stock or you are between fits.
How to Use
Take your measurements
Use a soft measuring tape and, for the most accurate result, wear a non-padded bra or none at all. For the underbust (band), wrap the tape snugly — not tight — around your ribcage directly under your bust, keeping it level. For the bust (full), measure around the fullest part without pulling tight.
Enter your numbers
Pick your Measurement Unit — centimeters or inches — then type both the underbust and bust values into the fields.
Calculate your size
Press Calculate Bra Size (or hit Enter) to see your bra size displayed across all six sizing systems at once.
Review and fine-tune
Check your main size, then explore the sister sizes and the fit tips tailored to your cup range to dial in the most comfortable fit.
Features
Six International Sizing Systems
See your size in US, UK, EU, FR, AU/NZ, and JP at the same time — handy when band numbering and cup letters differ between regions.
Centimeters or Inches
Switch the measurement unit to cm or inches; the calculator adjusts the input ranges and conversions to match.
Sister Size Suggestions
Get alternatives with the same cup volume, each labeled as a tighter or looser band so you can find a comfortable fit when your size is unavailable.
Personalized Fit Tips
Receive style and support advice tailored to a smaller, medium, or larger cup range to help you choose a flattering, comfortable bra.
Built-in Measurement Guide
Clear how-to-measure instructions show exactly where to place the tape for your underbust and bust, so your inputs are accurate.
Private and Instant
Results appear the moment you calculate, with everything processed locally in your browser — nothing is sent to a server.
Frequently Asked Questions
How do I measure my band size?
Wrap a soft tape snugly — not tight — around your ribcage directly under your bust, keeping it level and parallel to the floor. This underbust measurement determines your band. Enter it into the calculator in either centimeters or inches.
How do I find my cup size?
Your cup comes from the difference between your bust and underbust measurements — roughly one cup letter per inch (about 2.5 cm). You do not have to do the math yourself: enter both numbers and the calculator works out the cup letter for each sizing system.
What does a size like 34B mean?
The number is the band, which relates to your underbust measurement, and the letter is the cup, which reflects how much larger your bust is than your underbust. So 34B is a 34 band with a B cup. The calculator shows this band-and-cup pairing for all six systems.
Can I measure my bra size at home without help?
Yes. All you need is a soft measuring tape and the two measurements — underbust and bust. For the best accuracy, measure while wearing a non-padded, unlined bra or none at all, since padding adds volume and can throw off the bust reading.
What are sister sizes and why try them?
Sister sizes share the same cup volume but use a different band-and-cup combination — for example, 32C, 30D, and 34B. If a bra feels too tight in the band, try the sister size with a larger band and smaller cup letter; if it feels loose, try the one with a smaller band and larger cup letter.
How do US, UK, and EU bra sizes convert?
US and UK share the same band numbers but diverge in cup letters above D (US goes DD, DDD; UK goes DD, E, F, FF, G). EU uses centimeter-based band numbers (60, 65, 70, 75…) with letter cups, and FR adds 15 to the EU band. The calculator handles all of these conversions for you automatically.
How accurate is this calculator?
It uses standard industry formulas, so it is a reliable starting point — but real-world fit varies between brands and styles. Treat the result as a guide, try bras on to confirm, and lean on the sister sizes if your calculated size does not feel quite right.
Is my data private?
Yes. Every calculation happens entirely in your browser. Your measurements are never sent to a server, stored, or shared, so you can use the calculator with complete privacy.
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