Bra Size Calculator

Compute US bra size from band and bust measurements, with US ↔ UK ↔ EU conversion table.

Result

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How to use this calculator

Measure your underbust (band) snugly with the tape level.
Measure your full bust at the fullest point, with the tape level and not pulled tight.
Enter both numbers in inches or centimetres.
The US size + UK + EU equivalents appear together.
If two sister sizes are close, try both — a 34C and a 32D have the same cup volume but different band tension.

About this calculator

Bra sizing across the US, UK, and EU uses the same two underlying measurements (band and bust circumference) but reports cup letters and band numbers differently. The cup difference (bust minus band, in inches) maps to a letter — 1"=A, 2"=B, 3"=C, 4"=D — but the system diverges past D: the US uses DD, DDD, G, H, …; the UK uses DD, E, F, FF, G, GG, …. The band measurement is rounded up to the nearest even inch in the US and UK; the EU uses centimetres in increments of 5 (60, 65, 70, 75, 80…). This calculator applies the modern "no +4/+5 inches" rule recommended by Bratabase, Linda the Bra Lady, and most professional fitters — the older "add 4-5 inches to your underbust measurement" method consistently undersizes bands.

Frequently asked

Why am I a different cup size in UK vs US?+

Letters diverge past D. US: DD, DDD, G, H… UK: DD, E, F, FF, G, GG… For example, US "DDD" is UK "F". Bratabase publishes the canonical mapping.

Why is my "+4" measurement always too tight?+

The "+4 / +5 inches" method dates from the 1930s when bras had different elasticity. Modern bras stretch more, so adding inches consistently undersizes bands. The current standard from professional fitters (Linda the Bra Lady, A Bra That Fits subreddit) is to round band up to the nearest even inch only.

What is a "sister size"?+

A different band/cup pair with the same cup volume — moving up one band size requires going down one cup, and vice versa. Example: 34C and 32D have identical cup volume. Useful when one band is tight but the cup fits.

How accurate is the EU conversion?+

EU band sizes are quoted in cm at 5 cm increments. The conversion is an approximation; some EU manufacturers use 65/70/75 = 30/32/34 (subtract 35 cm), others use 70/75/80 = 32/34/36 (subtract 38 cm). This tool uses the dominant modern convention (band_cm = US_in × 2.54 − ~10).

Source for the conversion tables?+

Bratabase International Bra Size Converter; Linda the Bra Lady fitting guide; A Bra That Fits subreddit calculator; Bare Necessities international sizing chart.