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One accurate bra size, wherever you shop
Sizing labels change at every border — the same body can be a 34B, a 12, or a 75B depending on where you're standing. Enter two measurements and get your size across 16 regions, including the US, UK, EU, India and Japan, instantly.
Hold the tape snug and level under the bust, over a thin, unpadded bra.
Hold the tape loose and level across the fullest point, without pressing in.
We need both numbers before we can calculate anything.
All five calculated from your two measurements — JIS (Japan) uses its own centimetre-based formula, so treat it as an approximation.
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A schematic fit diagram, scaled to your cup size — not a photographic or anatomical rendering.
Cross-border conversion
See your size in every major system
Cross a border and the label changes, even if your body doesn't. The exact same fit reads as a 34B in the US and UK, turns into a 75B the moment you're in France or Germany, and takes on a completely different cup letter in Japan. Calculate above and watch your row light up below.
| US / UK | EU / France | Australia | Band (cm) |
|---|
The method
The maths behind your size
The old habit of tacking four or five extra inches onto your underbust belongs to a stiffer-fabric era that's long gone. Modern fit specialists work straight from the real number, and this calculator does the same.
Read the band
Pull the tape snug around your ribcage, directly beneath the bust, keeping it level all the way round. Round to the nearest whole number — that's your band, no padding added.
Read the bust
Loop the tape loosely across the fullest point of your bust. It should rest lightly, never squeezing or reshaping anything.
Work out the gap
Subtract band from bust. Every inch of that gap climbs one cup letter up the scale — one inch lands on A, two on B, three on C, and so on upward.
cup difference = round(bust, in) − band
0=AA · 1=A · 2=B · 3=C · 4=D · 5=DD/E · 6=F · 7=FF · 8=G
Worked example
Say your underbust reads 34″ exactly, so the band stays at 34. Your bust comes in at 38″, a 4-inch gap — that's a D cup, giving 34D. Can't find that exact size? The sister sizes 36C and 32DD carry almost the same cup volume.
Sizing around the world
How regional systems actually differ
Almost every country uses the same band-plus-cup logic — but the letters and numbers on the tag change depending on where the garment was made.
Band in inches, cup by inch difference
Band is the underbust in inches. Cup letters climb one per inch of bust-to-band difference: A, B, C, D, DD... US sizing keeps its own lettering above a D cup (DD, DDD/E, F...).
Same inch band, UK-style cup lettering
These markets share the same band-inch system and follow the UK cup progression — a US DD is a UK E, and it keeps shifting by roughly one letter as sizes go up. Most Indian and Singaporean retailers label bras this way.
Follows US band and cup lettering
Filipino retailers commonly stock and label bras using the US convention, including the US-style DD/DDD lettering above a D cup.
Band in centimetres
The same body's band converts roughly to a centimetre figure (a US/UK 34 is a EU 75). Cup letters generally follow the UK convention once converted.
Closest fit is the EU centimetre system
Neither has one single official national standard, but most retail sizing in China and Thailand maps closely to the EU centimetre band with UK-style cup letters.
Band and cup, both in centimetres
Japan's JIS standard, which South Korea's sizing closely follows, rounds the band to the nearest 5cm and measures the bust-to-band difference in centimetres — each 2.5cm of difference moves one cup letter, so these sizes don't translate one-to-one with a US or UK size.
Many countries across Asia don't have one single official standard and instead adopt whichever import convention (US, EU or Japan-style) their retailers use most — so treat any of these as your closest starting match, not a guaranteed national standard.
Our calculator above now supports 16 regions across three systems — pick a tab before calculating, and the result strip shows US, UK, EU, India and Japan side by side automatically.
Before you shop
Mistakes worth avoiding
Measuring over a padded style
Foam and moulded shapes quietly inflate the bust reading. Switch to a thin, unlined bra — or skip the bra entirely — before you measure.
Cinching the tape too hard
Firm is the goal, not tight. You should still be able to slip two fingers comfortably under the band once it's on.
Letting the tape drift
Check yourself in a mirror — it's easy for the back of the tape to creep upward without you noticing while you read the front.
Trusting a single import label
Sizing blocks shift from brand to brand and country to country. Use your calculated size as a launch point, then let fit make the final call.
Skipping past sister sizes
Exact size sold out, or almost-but-not-quite right? The sister size right next to it usually solves the problem without changing volume.
Assuming it's fixed forever
Weight shifts, a new training routine, pregnancy or nursing can all quietly move both numbers within a matter of months.
Video Guide
Watch: How to Measure Your Bra Size Correctly
Follow this step-by-step tutorial to accurately measure your band size and bust size before using the calculator. Accurate measurements help you find the best-fitting bra.
Questions
Frequently asked questions
Showing our top 15. See the full FAQ page for more, with search.
Yes. Bra Size is free worldwide with no sign-up, no app download and no region restrictions.
Close, but never exact — fabric stretch, wire shape and each brand's own cutting pattern all pull the final fit slightly. Use the number to shortlist sizes to try, not as gospel.
There has never been a single global standard above a D cup, so the US and UK diverged decades ago — a US DD is a UK E, and it keeps shifting by roughly one letter as sizes go up.
No. Japan's JIS standard measures cup difference in centimetres rather than inches, with each 2.5cm of difference moving one cup letter, so a Japanese size doesn't translate one-to-one with a US or UK size.
A neighbouring size that holds onto the same cup volume. Move the band up a notch and the cup down a letter — or the reverse — and the fit stays close to unchanged.
Roughly once or twice a year, and any time your shape shifts — after a change in weight, pregnancy, nursing or surgery.
Not a separate one — most Indian retailers use the same inch-band, UK-style cup lettering as the UK. Select the IN tab above to see it labelled that way.
Many Southeast Asian markets don't have one official national standard and instead follow whichever import convention — US, EU or Japan-style — their retailers stock most, so treat our result as your closest starting match.
Because no two manufacturers share a cutting block. A 34B at one counter can wear like a 34C at another — ordinary, and exactly the gap sister sizing exists to close.
Leave it out — that workaround dates back to stiffer, less forgiving fabric. Your actual underbust number, unpadded, is what modern fitters and this tool both use.
Only for a moment. A band with too much give rides up your back and pushes the support work onto your straps instead — level and snug on the loosest hook is what actually lasts.
The size label carries over, but wire-free and soft-cup styles often run a touch roomier, so some people go down a cup size when switching.
Easily — band and cup describe circumference and volume, not shape. Two people in the identical labelled size can still differ widely in root width and projection.
Check the sister sizes alongside your result — same cup volume, different band, and typically far easier to actually find in stock.
Yes — a thin, unpadded bra, a natural stance in front of a mirror, and a tape kept level front to back is really all it takes.
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