Bra Size Calculator
Estimate a bra size from underbust and bust measurements in inches or centimetres. Returns an even US band and cup (34B), or the UK or EU size, or the two sister sizes with the same cup volume.
Last updated: October 2026
Bra Size
32D
This calculator gives an estimate for general information only. It is not medical advice and does not replace a doctor, pharmacist or other qualified health professional. Always check with them before acting on the result, especially for medication doses, children, pregnancy or a medical condition, and follow the guidelines of your local health authority.
Formula below · 2 sources (ncbi.nlm.nih.gov, nordstrom.com) · Updated Oct 2026
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About this calculator
US bra sizing pairs a band size in inches (measured around the ribcage just under the bust) with a cup letter based on the difference between the bust measurement and the band measurement. A 1-inch difference is roughly an A cup, 2 inches a B, 3 inches a C, 4 inches a D, and so on up through DD, DDD/E, F, G, and beyond.
This calculator uses the modern 'true fit' rule: band inches ≈ underbust inches. US bands come in even sizes only (28, 30, 32, 34 …), so the underbust is rounded to the nearest even number, and an odd measurement that falls exactly between two bands rounds up (31 in → 32 band). The cup is then the bust minus that band. Older '+4' or '+5' methods added inches to the underbust to derive the band and are now considered inaccurate — they systematically produce a too-loose band, which fit specialists say is the root cause of most 'my bras don't fit' complaints.
Metric measurements: choose centimetres and the calculator divides by 2.54 before applying the same rule, so 81 cm underbust and 91 cm bust is 32 in and 36 in, a 32D.
Other systems. UK sizes use the same band inches but different cup labels above D: US DD = UK DD, US DDD = UK E, US G = UK F, US H = UK FF, US I = UK G, then GG, H, HH, J, JJ. EU sizes number the band in steps of 5 (65, 70, 75 …), nominally the underbust in centimetres the band is cut for, and the charts line up US 32 = EU 70, 34 = 75, 36 = 80, 38 = 85 (EU band = US band × 2.5 − 10); the EU band number is lower than the US underbust in centimetres because US band numbers still carry the old +4 convention. EU cups are single letters for every step (A, B, C, D, E, F, G …), so a US 32DDD is an EU 70F. Choose the UK or EU view to see these.
Sister sizes. Going down one band and up one cup keeps the same cup volume, and so does going up one band and down one cup: 32D, 30DD and 34C all hold the same breast. The sister-size view lists both neighbours; try the smaller band if the band rides up at the back, the larger if it digs in.
Cup difference (bust minus band, inches) in US, UK and EU cup letters
Scroll sideways to see all columns →
| Difference (in) | US cup | UK cup | EU cup |
|---|---|---|---|
| 0 | AA | AA | AA |
| 1 | A | A | A |
| 2 | B | B | B |
| 3 | C | C | C |
| 4 | D | D | D |
| 5 | DD | DD | E |
| 6 | DDD | E | F |
| 7 | G | F | G |
| 8 | H | FF | H |
| 9 | I | G | I |
| 10 | J | GG | J |
How to use
Example — a fitting session. Underbust 32 in, bust 36 in. Enter underbust = 32, bust = 36. Band = 32 (already even); cup difference = 36 − 32 = 4 → D. Result: 32D. Try that size on. If the band rides up in back, size down one band and up one cup (30DD) — those 'sister sizes' have the same cup volume in a tighter band. Choose "US size with sister sizes" and the calculator prints 32D (sister sizes 30DD and 34C). Example — metric. Underbust 81 cm, bust 91 cm, units set to centimetres. 81 ÷ 2.54 = 31.9 in → band 32; 91 ÷ 2.54 = 35.8 in; cup difference = 36 − 32 = 4 → D. Result: 32D; EU view: 70D; UK view: 32D. Example — larger frame. Underbust 38, bust 44. Band = 38 (even); cup diff = 6 → DDD. Result: 38DDD (UK 38E, EU 85F). Sister sizes in either direction (36G/40DD) may also fit if the band comfort is off. Example — odd underbust. Underbust 31, bust 35. There is no 31 band, so the band rounds up to 32; cup diff = 35 − 32 = 3 → C. Result: 32C (sister size 34B).
Frequently asked questions
How do I measure correctly?
Wear a well-fitting non-padded bra. For underbust, run the tape snugly under the bust and around the ribcage, level all the way around, and note the number of inches. For bust, run the tape across the fullest part of the bust, keeping it level. Both measurements should be taken with a normal breath. If your bust measurement changes by more than an inch when you inhale, take the exhale reading.
What are 'sister sizes'?
Sister sizes have the same cup volume but a different band. Going down one band and up one cup preserves cup volume: 34B, 32C, 30D, 28DD all have the same-size cup. If a 34B fits the cup but the band feels tight, try 36A. If it fits the cup but the band is too loose, try 32C. Sister sizing is the fastest way to iterate on fit without changing brands.
How do I convert my US size to UK or EU?
The band is the same number in the UK (inches) and steps by 5 in Europe: US 32 = EU 70, 34 = 75, 36 = 80, 38 = 85. Cups match up to D; above that US DD = UK DD = EU E, US DDD = UK E = EU F, US G = UK F = EU G, US H = UK FF = EU H. Choose the UK or EU view and the calculator does this for your measurements.
Does the calculator work for sports bras or teens?
The measuring rule is the same: snug underbust for the band, fullest-point bust for the cup. Many sports bras are sold in S/M/L instead, mapped from the band and cup on the brand's chart (a 32D is often an M). For teens, bodies change fast, so re-measure every few months; the method is identical, and a small cup difference simply gives an AA or A.
Why do brands fit so differently?
There is no legally binding US bra sizing standard. Each brand's cup shape, wire width, and gore height (the piece between the cups) differs, so a 34C in one brand can feel like a 32D or 34B in another. Use the calculator's number as a starting point and iterate. Sister sizing (see above) is your friend.
How often should I remeasure?
Whenever weight or torso size changes materially — pregnancy, post-partum, weight loss/gain of more than 10 lb, hormonal changes — because both band and cup can shift. Fit specialists also recommend a fresh fitting every 6–12 months even without body changes because bras stretch out and lose support with wear.
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