Enter your bust and underbust measurements to calculate your bra size, with instant equivalents in US, UK, EU, French and Australian sizing.
Lingerie • US/UK/EU/FR/AU
Two tape measurements produce your size in US, UK, EU, French and Australian sizing at once, with the primary result highlighted so a pattern in any of them can be followed directly.
Results are recalculated on every keystroke, with no submit step and no page reload, so a value can be adjusted until the answer looks right rather than guessed once.
Everything runs in your browser — no account, no uploads, nothing leaves your device.
A bra size combines two measurements: the band (the firm circumference around your ribcage, directly under the bust) and the cup (the difference between your bust and your band). The lettered-cup system was introduced by S.H. Camp and Company in 1932 and popularised by Warner's, and is now expressed differently around the world.
How this calculator works. Your underbust measurement is rounded to the nearest even inch to give the band (e.g. 31″ → 32). The cup is then taken from how many inches your bust is larger than your band: each inch is one cup up — about 1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD, 6″ = DDD/F, and so on. The result is then expressed in US/Canada, UK, EU (EN 13402), France/Spain and Australia/New Zealand standards. For example, a 32″ band with a 36″ bust is a US 32D, UK 32D, EU 70D and French 85D.
Because every brand and style fits a little differently, treat the result as an accurate starting point rather than a guarantee — if a band feels tight or loose, try the "sister size" (go down a band and up a cup, or up a band and down a cup) for the same cup volume.
Bra sizing combines a band measurement with a cup letter, and the cup is not an absolute volume — it is the difference between bust and band. That makes cup letters relative: a 32D and a 36D have the same four-inch difference but very different cup volumes. The practical consequence is sister sizing, where going down a band size requires going up a cup letter to preserve the same cup volume. Systems also differ internationally: UK, US and EU use different band numbers and diverge in cup lettering above D, which is where most conversion errors occur.
Band = underbust measurement (US traditionally added 4–5 inches; modern fitting does not)Cup = bust measurement − band measurement, 1 inch per cup letterSister size: band −1, cup +1 preserves cup volumeEU band = UK band inches × 2.54, rounded to the nearest 5where:
Assumptions: The older US practice of adding 4–5 inches to the underbust is now widely considered incorrect and produces bands that are too loose. Professional fitting is recommended; band and cup interact, so a poor fit in one is often misdiagnosed as the other.
Work from two measurements, then derive sister sizes for a different band.
Result32D — sister sizes 30DD and 34C hold the same cup volume
Sister sizing is the practical tool when a band feels wrong but the cup fits: change both together rather than one. Note that US and UK cup lettering diverges above D — a UK DD is a US E — which is the single most common error when ordering across markets.