Free bra size calculator
Enter your underbust and bust measurements to calculate your starting bra size in seconds.
Bra size calculator
Use inches or centimeters and get US, UK, EU, French, and AU/NZ size results with sister-size guidance.
You need two measurements:
Measure around your ribcage directly under your bust. Keep the tape level and snug.
Measure around the fullest part of your bust. Keep the tape straight and relaxed.
Tip: Use a soft measuring tape and measure without thick clothing or padding.
Bra sizing is not perfectly standardized across brands. Your result gives you the best measurement-based starting point, then you can adjust using fit checks, sister sizes, and brand size charts.
Measurement guide
Use these quick steps before entering your underbust and bust measurements.
Wrap the tape snugly around your ribcage, directly under your bust. Keep it level across your back.
Measure around the fullest part of your bust. Keep the tape relaxed, straight, and comfortable.
Enter both measurements, choose inches or centimeters, and select your sizing region for a starting size.
Need more detail? Read the full guide on how to measure bra size.
This calculator estimates your bra size from two measurements:
The difference between your bust and band measurements helps determine the cup letter. Your selected country changes the size label because US, UK, EU, French, and AU/NZ systems use different band and cup naming rules.
Understand the result
A bra size combines a band number and a cup letter.
For example, in 34C:
Cup letters are not fixed volumes by themselves. A 34C and 36C do not have the exact same cup volume because cup size changes with band size.
Fit check
The band should feel snug and stay level around your body.
The cup should contain breast tissue without gaping, spilling, or cutting in.
The center gore and underwire should sit comfortably without pressing on breast tissue.
Troubleshooting
Your result is a starting point. If the first size does not feel right, use these checks:
Try a smaller band size, or a sister size with a smaller band and larger cup.
Try a larger cup size, or check whether the cup shape is too shallow.
Try a smaller cup, a different cup shape, or a sister size depending on how the band feels.
The band may be too loose, causing the straps to carry too much weight.
Try a larger cup, a wider wire, or a cup shape with more room where your tissue sits.
More detail
The standard calculator uses two measurements: underbust and bust. That works well for a quick starting size.
The advanced bra size calculator uses six measurements to better account for breast projection, fullness, tissue distribution, and measurement variation.
Measure your underbust directly under your bust, then measure around the fullest part of your bust. Enter both measurements into the bra size calculator, choose inches or centimeters, and select your sizing region to estimate your starting band and cup size.
The calculator gives a measurement-based starting size, not a guaranteed final fit. Bra fit can still change by brand, fabric, wire width, cup shape, and personal comfort.
Use whichever unit is easiest for you. The bra size calculator works in inches and centimeters, as long as you use the same unit for both underbust and bust measurements.
US and UK bra sizing use different cup-label progressions, especially after D. Your body measurements can be the same while the displayed size label changes by region or brand.
Treat the result as a strong starting size. Bra fit still depends on brand, cup shape, wire width, fabric, and personal comfort, so use fit checks and sister sizes if the first result is close but not perfect.
Sister sizes are nearby sizes with similar cup volume but different band sizes. For example, if the cups feel close but the band is too loose, a smaller-band sister size can help.
Start with the size closest to your measurements, then compare the fit. If the band feels wrong but the cups are close, use sister sizing; if the cups spill or gape, adjust cup size or cup shape.
Yes. The calculator uses the difference between bust and band measurements to estimate cup size, then combines that cup estimate with your band size and selected sizing region.
Related tools
Use six measurements for a more detailed fit check when the standard result feels close but not quite right.
Open Advanced bra size calculatorFind nearby sizes when your cup volume feels close but the band needs adjusting.
Open Sister size calculatorCompare band and cup labels across common sizing systems before shopping.
Open Bra size chartConvert sizes between US, UK, EU, French, and AU/NZ labels.
Open Bra size converterLearn what band numbers and cup letters mean in real fit terms.
Open Bra size meaningsFollow the full measuring tutorial if you want more detail before using the calculator.
Open How to measure bra sizeUse an inches-focused calculator page when you prefer US-style measurements.
Open Bra size calculator in inches