Bra Size Calculator

Two measurements — a starting band and cup size estimate.

in
in

Underbust: firm tape directly under the breasts. Bust: loose tape around the fullest part, wearing a non-padded bra.

Estimated size (US)
34C
Cup difference
4.0 in

This gives a measurement-based starting point, not a guaranteed fit — cup volume and band comfort still vary by brand, wire shape, and style. Try a few sister sizes if the first result feels off.

A worked example

A 33-inch underbust with a 37-inch bust rounds to a 34 band, with a 4-inch cup difference — a 34C.

Frequently asked questions

Why does band size always round to an even number?

US and UK bra bands are traditionally only manufactured in even-numbered sizes (32, 34, 36...) — an odd-number measurement gets rounded up to keep it within that standard sizing range.

What's a 'sister size'?

A nearby size with a different band but the same cup volume — going down a band size while going up a cup size (or vice versa) roughly preserves the cup volume, which is useful if a size feels close but not quite right in the band.

How often should I re-measure?

Body composition changes — from weight fluctuation, exercise, hormonal changes, age, or pregnancy — can shift bra size meaningfully, so re-measuring roughly every six months to a year is commonly recommended.

This calculator estimates a starting size based on common measurement methods; cup volume and band comfort still vary by brand, wire shape, and style, so use the result as a guide rather than a guarantee.