Bra Size Calculator

Frequently Asked Questions

How do I measure for a bra size at home?

Use a soft tape measure. Measure underbust (snug, just under the chest) and bust (loosely, at the fullest point). The difference in inches gives cup size: 1 in = A, 2 in = B, 3 in = C, 4 in = D, 5 in = DD.

What is a sister size?

A sister size has the same cup volume but a different band. Going up a band and down a cup (e.g., 34C to 36B) keeps the same volume with a looser fit around the ribcage. Useful when a style runs tight or loose in the band.

Why does my size differ between brands?

There is no universal bra sizing standard. Each brand uses its own grading, fabric, and construction. The calculated size is a starting point - always check a brand's own fit guide and read reviews about whether a style runs large or small.

How often should I re-measure?

Annually is a good baseline, or any time your weight changes by more than about 10 pounds, after pregnancy or nursing, or if your current bras stop feeling comfortable. Bodies change and so do bra sizes.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Measure your underbust (the circumference directly under your breasts, snug but not constricting) and your full bust (the fullest part of your chest, measured loosely). The band size is derived from the underbust measurement, rounded to the nearest even number in the US system. The cup size comes from the difference between bust and band: each inch of difference equals one cup letter, starting at A for a 1-inch difference. Enter both measurements and the calculator converts them into US, UK, EU, and FR sizes simultaneously.

How to Measure Correctly

Use a soft measuring tape. For underbust, wrap it flat against your skin just under your chest, keep it level all the way around, and breathe out normally before you read the number. For bust, drape the tape across the fullest part of your bust, standing upright with a relaxed, natural posture. Measure in inches or centimetres - the calculator handles both. If you get an odd underbust number and you are between sizes, go up one inch if you prefer a looser band or keep it if you like a firm fit. Bra sizing is more of a starting point than a precise science, and fit varies widely by brand and style.

Understanding Cup Sizes

Cup size describes the volume difference between your bust and your band, not an absolute volume. The same cup letter on a larger band holds more volume than on a smaller band. A 32D and a 36B have roughly the same cup volume - these are called sister sizes. Going up a band size and down a cup size (or vice versa) gives you the same cup volume with a different fit across the ribcage. Sister sizes are useful when a style runs large or small in the band, or when you are between standard sizes.

Size Equivalents Across Systems

US bra sizing uses a numeric band (32, 34, 36...) and letter cups (A, B, C, D, DD/E, DDD/F). UK sizing uses the same scale but different labelling past D - UK DD is the same as US DD, but US DDD is UK E and US G is UK FF. EU sizing adds 10 to the US band number (US 34 = EU 75) and uses numeric cups starting at A=AA, B=A, C=B, D=C. French (FR) sizing is similar to EU. The calculator outputs all four so you can shop international brands without the confusion.

Signs Your Bra Does Not Fit

Band riding up: band is too large - go down a size and adjust cup accordingly.

Underwire digging in or poking: cup is too small or the underwire shape does not match your body.

Straps digging in: straps are doing the lifting work that the band should do - usually a band too loose.

Gaping cups: cup is too large, try a smaller cup or a sister size with a smaller band.

Spillage at the top or sides: cup is too small - go up one or more cup sizes.

Centre gore not lying flat: classic sign of a cup too small.

Tips for a Better Fit

Always try before committing to a size. Bra sizing standards vary by country and brand - some European luxury brands size several cups smaller than US equivalents. Re-measure every year or any time your weight changes significantly. When you first buy a bra, fasten it on the loosest hook so the band can be tightened as the elastic stretches over time. If underwire bras are uncomfortable, soft-cup or wire-free styles in the correct size often provide similar support with greater comfort.

Bra Size Calculator

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