Bra Size Converter — JP, US, UK, EU & FR
Convert bra band and cup sizes between JP, US, UK, EU and FR, or calculate your JP size from underbust and bust measurements in cm — with band and cup charts and notes on where systems diverge.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
Sizes are standards-based approximations — brands and even product lines vary a lot, so try on when possible. UK cups match US only up to D; above D they diverge (US DD/DDD… vs UK DD/E/F…), and JP cups run one step earlier than US (JP B ≈ US A).
Band chart
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Cup chart
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About this tool
Bra sizing is notoriously fragmented: bands in centimetres here, inches there, and cup letters that mean different things in different countries. This bra size converter maps sizes between the JP, US, UK, EU and FR systems — a Japanese C75 corresponds to a US 34B/34C territory, an EU 75C, a FR 90C — and includes a measure mode: enter your underbust and bust measurements and it suggests a starting size in every system. All tables and calculations are built into the page and run in your browser, so these very personal numbers are never sent or stored anywhere.
Frequently asked questions
What are sister sizes?
Sister sizes are different band-and-cup labels that hold roughly the same breast volume. The rule: go up a band, down a cup (75C → 80B) or down a band, up a cup (75C → 70D). Cup letters only have meaning relative to the band, which is why a 70D is not "bigger" than an 80B. Sister sizes are the standard trick when a style is sold out in your size, or when the band feels right but the brand runs tight or loose — adjust one step and try again.
Why does my size differ between brands and countries?
Because the systems disagree and so do the makers. US and UK cups diverge above D (UK uses DD, E, F…; US brands vary), French bands run 15 higher than EU ones for the same body, and Japanese cups are graded in 2.5 cm steps against inch-based systems. On top of that, each brand drafts its own patterns, and stretch, padding and cut change the fit. Use any conversion — including this one — as a standards-based starting point, then check the brand's own chart and fit guide.
How do I measure myself for the measure mode?
You need two numbers. Underbust: wrap a soft tape measure snugly around your ribcage directly under the breasts, level all the way round, and exhale normally. Bust: measure around the fullest point, tape parallel to the floor, ideally in a light non-padded bra. Stand straight, don't pull the tape tight enough to dig in, and repeat once to confirm. Bodies change with weight, hormones and time of month, so re-measure every few months. The numbers are processed locally and never leave your browser.