How do I measure my bra size at home?

Use a soft measuring tape while wearing an unpadded bra or none at all. For the band, wrap the tape directly under your bust, snug and level all the way around, and breathe out normally. For the bust, measure loosely around the fullest point without compressing anything. Measure twice — the tape drifting even half an inch changes the result.

What is a sister size in bras?

A sister size holds the same cup volume in a different band: 32D, 34C, and 36B all hold roughly the same amount. If a bra's cups fit but the band is too tight, go up a band and down a cup letter; if the band rides loose, go down a band and up a letter.

Why is my bra size different in every brand?

There is no enforced sizing standard, so cut, fabric stretch, and country conventions all shift the fit — a US DDD is a UK E, and many US brands label DDD as F. Treat any calculated size as a starting point and let the fit checks (level band, flat center panel, no spillage or gaping) make the final call.

How can I tell if my bra fits correctly?

The band should sit level around your body, snug enough that you can slide only about two fingers under it — the band does most of the supporting, not the straps. The center panel should rest flat against your sternum. If the band rides up your back, it's too big; if breast tissue spills over or the cup gapes, adjust the cup size.

How often should I re-measure my bra size?

About once a year, and any time your body changes — weight shifts, pregnancy, nursing, new training habits, or hormonal changes can all move your size. Bands also stretch with wear, so a bra that fit perfectly a year ago may now fit like its looser sister size.

Bra Size Calculator — US, UK & EU Sizes + Sister Sizes

Choose inches or centimeters, then enter a snug underbust measurement and a relaxed bust measurement. You'll get your US bra size, the UK and EU equivalents, and both sister sizes.

How to measure for a bra size

Two measurements, taken honestly, are all this needs. Underbust: wrap a soft tape directly under your bust, level all the way around, snug but not digging in — this is where the band sits, and the band does most of the work. Bust: measure around the fullest point, standing relaxed, wearing an unpadded bra or none at all (padding adds phantom inches). Don't hold your breath, don't cinch the tape, don't round toward the size you'd prefer. The tape has no opinions about you, and neither does this calculator.

The formula

Band = underbust rounded to the next even number | Cup = bust − band, one letter per inch

This calculator uses the standard US method. Your underbust is rounded to the nearest whole inch (halves round up), and odd numbers round up to the next even band — 31″ becomes a 32 band. The cup is the bust-minus-band difference rounded to the nearest inch: under 1″ is AA, then 1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD, 6″ = DDD (which many US brands label F), 7″ = G, 8″ = H. UK sizes share the same band numbers but the cups diverge after DD (E, F, FF instead of DDD, G, H), and EU bands are your underbust in centimeters rounded to a multiple of 5 — a US 34 band is roughly an EU 75.

Worked example

Underbust 31″, bust 36″:

31 is odd, so the band rounds up to 32. The difference is 36 − 32 = 4″, which is a D cup. Result: US 32D, which is also a UK 32D and an EU 70D — with sister sizes 30DD (snugger band, same cup volume) and 34C (looser band, same cup volume).

Sister sizes: the most useful bra fact nobody explains

Cup letters are not absolute volumes — they're relative to the band. A D cup on a 32 band holds about the same as a C on a 34 or a B on a 36. That's what sister sizes are: same cup volume, different band length. This matters because when a bra feels wrong, the instinct is to change the cup letter, when the real fix is usually sliding along the sister-size chain. Band digging in but cups fine? Go up a band, down a letter. Band riding up your back? Down a band, up a letter — a band that rides up is too big, full stop.

Take the number as a starting point

You'll often read that 80% of women wear the wrong bra size. The figure is repeated everywhere but traces back to small surveys and industry sources, so hold it loosely — though the pattern behind it (band too big, cup too small) is real and worth checking for. And because there's no enforced sizing standard, the same measurements land differently across brands and countries. Use your result here as the size to try on first, then trust the fit checks: band level and snug, center panel flat against your sternum, no spillage over the cup and no gaping under it. If your measurements fall outside standard charts, a free fitting at a specialty lingerie shop is genuinely worth it — that's expertise, not failure.

Bra Size Calculator