Bra Size Calculator
Enter your underbust and bust measurements once. BraFitly provides a measurement-based starting size and common equivalents for UK, US, EU, French, Australian/NZ, Canadian and Indian sizing systems.
Calculate your bra size
Use a soft measuring tape and enter both measurements in the same unit.
Your measurements are processed in this browser for the calculation. No account is required.
Explore the BraFitly sizing guides
The homepage is the calculator hub. Detailed search topics live on their own pages so each guide can answer a specific question without repeating the full homepage.
How to Measure Bra Size
Step-by-step instructions for measuring your underbust and bust accurately at home.
Read the measurement guide →Bra Size Chart
Understand band and cup sizing and compare common international references.
View the bra size chart →Sister Size Calculator
Find nearby sister sizes when the band or cup of your current size needs adjustment.
Calculate sister sizes →International Converter
Compare common UK, US, EU, France, Australia/NZ, Canada and India references.
Convert a bra size →Bra Fit Check
Learn how the band, cups, straps, underwire and centre gore should fit.
Check your bra fit →Pregnancy & Nursing
Use dedicated current-size calculators for pregnancy, nursing and postpartum shopping.
Open pregnancy calculator →Open nursing calculator →
How BraFitly calculates an estimate
A transparent measurement-based model, not a claim of a universal or brand-specific fit.
- The underbust is converted to centimetres and mapped to the nearest even-inch UK/US-style band starting point.
- The cup estimate uses the bust-to-band difference and a reference cup sequence. This produces a starting point, not a guaranteed fit.
- International equivalents are mapped using reference conversion conventions. Systems and brands can differ, so conversion is not universal.
- Fit should always be confirmed against the garment manufacturer's current chart and the actual fit.
Reference material: Triumph international size charts and Triumph bra fitting guidance. Indian sizing references were also checked against Clovia's Indian bra size calculator and amante's India size guide. These brands are independent references and are not affiliated with BraFitly.
Last reviewed: August 28, 2026
Frequently asked questions
Quick answers here; detailed guides are available on the dedicated pages.
Why do many women wear the wrong bra size?
Bra sizing is not standardized across brands, bodies change over time, and many people rely on an old size or an inaccurate measurement. Use the calculator as a starting point and check actual fit.
What are sister sizes and why do they matter?
Sister sizes have similar cup volume with a different band and cup label. They can help when your current band feels too tight or too loose, but they are not a substitute for checking the fit.
How often should I re-measure?
Re-measure when your current bra stops fitting comfortably or after meaningful body changes. There is no single schedule that fits everyone.
Why does the same size fit differently across brands?
Brands and styles can differ in cup shape, wire width, fabric stretch, grading and fitting method. Always compare the brand's current size chart.
How does pregnancy change bra size?
Breast and ribcage measurements can change during pregnancy. Use current measurements rather than automatically adding a size. BraFitly's pregnancy tool estimates your current starting size and does not predict future changes.
What is the difference between US and UK cup sizes?
UK and US systems use different cup sequences after D/DD. For example, a UK E commonly corresponds to US DDD in reference charts. Individual brands can vary.
My underbust is an odd number — what do I do?
Measure again to make sure the tape is level and comfortably firm. The main estimate maps the measurement to the nearest even-inch band starting point, but the manufacturer's chart should be the final check.
What is the centre gore and why does it matter?
The centre gore is the part between the cups. In many underwire styles it should sit comfortably against the sternum without digging or forcing breast tissue out of the cups.