Bra size calculator: band and cup from underbust and bust in inches or cm, in US, UK, EU, FR/BE and AU sizes, with sister sizes and the method stated.
By AdminDrafted with AI writing toolsUpdated Checked examples: 6
Your measurements give a US 32DD by the plus-zero method (band = underbust to the nearest even inch). The same size is UK 32DD, US 32DD, EU 70E, FR/BE 85E and AU/NZ 10DD. Sister sizes with the same cup volume are 30DDD and 34D.
| US | UK | EU | FR/BE | AU/NZ | |
|---|---|---|---|---|---|
| 2 bands down | 28G | 28F | 60G | 75G | 6F |
| 1 band down | 30DDD | 30E | 65F | 80F | 8E |
| Your size | 32DD | 32DD | 70E | 85E | 10DD |
| 1 band up | 34D | 34D | 75D | 90D | 12D |
| 2 bands up | 36C | 36C | 80C | 95C | 14C |
An odd whole number, exactly between two even bands, is rounded up.
0 in = AA, 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD (Triumph UK); halves round up.
UK 32DD = US 32DD = EU 70E = FR/BE 85E = AU/NZ 10DD. Each 2-inch band step is 5 cm: UK 32 = EU 70 = FR/BE 85 = AU/NZ 10.
Band size comes from the snug measurement around the ribcage under the bust, and cup size from how much the bust measurement exceeds the band. The default plus-zero method, used in Triumph's UK fitting guide, rounds the underbust to the nearest even inch and counts one cup per inch of difference: 0 is AA, 1 A, 2 B, 3 C, 4 D and 5 DD. The traditional plus-four method and the European standard EN 13402, which works in centimeters, are the other two options.
An underbust of 31.5 inches and a bust of 37 inches give a 32 band and a 5-inch difference, a US and UK 32DD. The same size is a 70E in European sizes, 85E in French and Belgian sizes and 10DD in Australia, from the Fantasie and Freya conversion charts.
Brands size differently and the methods disagree by one or two band sizes, so treat the result as a starting point for a fitting. The sister sizes hold the same cup volume on a band one size up or down.
Round your underbust, measured snugly around the ribcage under the bust, to the nearest even inch for the band. Subtract the band from your bust measurement: each inch is one cup, 0 for AA, 1 A, 2 B, 3 C, 4 D and 5 DD. A 31.5 in underbust and 37 in bust give a 32DD.
This is the plus-zero method from the Triumph UK fitting guide. Brands and styles fit differently, so treat the result as the size to try on first.
An odd whole-inch underbust sits exactly between two bands and rounds up, so 33 in becomes a 34 band. A difference ending in half an inch also rounds up to the next cup.
This chart holds the UK/US band at 34. Each row is the same cup in every system. The letters match through D and split apart above it, so a UK 34E is a US 34DDD and an EU 75F.
| UK cup, band 34 | US | EU | FR/BE | AU/NZ |
|---|---|---|---|---|
| AA | 34AA | 75AA | 90AA | 12AA |
| A | 34A | 75A | 90A | 12A |
| B | 34B | 75B | 90B | 12B |
| C | 34C | 75C | 90C | 12C |
| D | 34D | 75D | 90D | 12D |
| DD | 34DD | 75E | 90E | 12DD |
| E | 34DDD | 75F | 90F | 12E |
| F | 34G | 75G | 90G | 12F |
| FF | 34H | 75H | 90H | 12FF |
| G | 34I | 75I | 90I | 12G |
| GG | 34J | 75J | 90J | 12GG |
| H | 34K | 75K | 90K | 12H |
| HH | 34L | 75L | 90L | 12HH |
| J | 34M | 75M | 90M | 12J |
| JJ | 34N | 75N | 90N | 12JJ |
| K | 34O | 75O | 90O | 12K |
Bands follow the Fantasie size guide: UK/US 32 is EU 70, FR/BE 85 and AU/NZ 10. Each band step adds 2 in UK/US and AU/NZ sizes and 5 in EU and FR/BE sizes.
Cup sequences follow Wacoal's size charts. The published charts cover bands 28 to 44; sizes outside that range extend the same steps.
The traditional plus-four method drops any fraction of an inch from the underbust, then adds 4 to an even number or 5 to an odd one. A 30.8 in underbust becomes 30 + 4 = 34, and with a 36 in bust that is a 2 in difference: a 34B.
Plus zero puts the same ribcage on a 30 band with a 6 in difference: UK 30E, or US 30DDD. The two methods can land several band and cup sizes apart, so compare sizes only within one method.
The historical EN 13402-3:2004 convention (standard excerpt) rounds the underbust to the nearest 5 cm for the band. The cup comes from bust minus the actual underbust, not the rounded band, in 2 cm steps.
AA is 10 to 12 cm, A 12 to 14, B 14 to 16, C 16 to 18 and D 18 to 20, continuing to H at 26 to 28 cm. A difference exactly on a boundary takes the larger cup.
An 89 cm underbust and 108 cm bust differ by 19 cm, which is D, on a 90 band: EU 90D, or UK 40D. Current European brands may use their own fitting rules, so the standard's label does not guarantee the same fit.
Sister sizes keep the cup volume on a different band: one band down and one cup up, or one band up and one cup down. The b.tempt'd fitting guide gives 32C and 36A as the sisters of a 34B.
The 32DD above has US sisters 30DDD and 34D. Try one when the cups fit but the band feels tight or loose; keeping the same letter on a different band changes the cup volume instead.
For dress, shirt and other garment sizes, use the clothing size converter; a clothing size cannot stand in for the two bra measurements.
Checked against: Triumph UK method: 31.5 → 32 band, 37 − 32 = 5 in = DD; conversions from the Fantasie chart (UK DD = EU/FR E = AU DD = US DD; 32 = EU 70 = FR 85 = AU 10)
Checked against: EN 13402 summary: 108 − 89 = 19 cm = D, 89 → 90, size 90D; EU 90 = UK 40 = FR 105 on the Fantasie chart
Checked against: b.tempt'd by Wacoal: “If you're usually a 34B, your sister sizes would be 32C and 36A”
Checked against: Plus-four rule as described in Wikipedia's Bra size article: even underbust + 4 = 34; 36 − 34 = 2 in = B
Measure snugly around the ribcage directly under the bust for the band, and around the fullest part of the bust for the cup, with the tape level. Triumph's UK guide rounds the underbust to the nearest even inch, then subtracts that band from the bust: each inch is one cup. A 33.5-inch underbust and 37-inch bust give a 34 band and a 3-inch difference, a 34C.
Sister sizes share the same cup volume on a different band: go up one band size and down one cup, or down one band and up one cup. Wacoal's b.tempt'd fit guide gives 32C and 36A as the sister sizes of a 34B. They help when a band feels too tight or loose but the cups fit, or when a style doesn't come in your usual size.
The plus-four rule adds 4 inches to an even underbust and 5 to an odd one, so a 30-inch ribcage wears a 34 band. Wikipedia's Bra size article records Kohl's using it in 2013. Triumph's UK guide instead rounds the measured underbust to the nearest even inch, which for a 30-inch ribcage and 36-inch bust gives a 30E instead of the plus-four 34B.
Bands follow a fixed pattern: UK and US 32 is 70 in Europe, 85 in France and Belgium and 10 in Australia, and each band step adds 5 cm. Cups match up to D; after that the UK uses DD, E, F, FF, the US DD, DDD, G, H, and Europe E, F, G, H, one letter per step, according to the Fantasie and Freya charts. A UK 34E is a US 34DDD and an EU 75F.
EN 13402 labels a bra with the underbust in centimeters, rounded to the nearest 5, and a cup letter from the difference between bust and underbust in 2 cm steps: AA is 10–12 cm, A 12–14, B 14–16, C 16–18 and D 18–20. An 89 cm underbust and 108 cm bust have a 19 cm difference, so the standard's size is 90D, which converts to a UK 40D.
This calculator includes 6 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.