Bra Size Calculator: Find Your True Size
Most people wear the wrong bra size — usually a band that’s too big and a cup that’s too small. Store fittings are inconsistent, and the old “add 4 inches” rule is outdated.
This free calculator uses the multi-measurement method fitting specialists trust: three underbust readings to pin down your band, three bust readings to pin down your cup — in US, UK, or EU sizing. Enter your numbers, get your size plus sister sizes and fit notes, then shop top-rated bras in your exact size on Amazon.
What Is My Bra Size?
Six quick measurements beat the old two-measurement guess. This is the same multi-measurement method fitting specialists use: three underbust readings pin down your band, three bust readings pin down your cup — in US, UK, or EU sizing.
Units
Sizing system
Step 1 — Underbust (3 measurements)
Wrap a soft tape around your ribcage directly under your bust. Keep it level and breathe normally.
Tape just resting — not digging in at all.
As snug as you’d want a bra band to feel.
As tight as you can comfortably pull it.
Step 2 — Bust (3 measurements)
Measure around the fullest part of your bust each time.
Standing straight, tape loosely around the fullest part.
Bend over 90° and measure loosely around the fullest part.
Lying on your back, measure loosely around the fullest part.
Your bra size
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How to take the 6 measurements
You’ll need a soft measuring tape and a mirror. Measure in inches or centimeters — the calculator handles both.
Underbust (3 readings)
- Loose: wrap the tape around your ribcage directly under your bust, just resting — not digging in at all.
- Snug: pull it as snug as you’d want a bra band to feel. Breathe normally.
- Tight: pull as tight as you comfortably can. This is your “can’t go smaller than” number.
Bust (3 readings)
- Standing: stand straight, tape loosely around the fullest part of your bust.
- Leaning: bend forward 90 degrees and measure loosely around the fullest part — this catches volume the standing reading misses.
- Lying: lie on your back and measure loosely around the fullest part.
Keep the tape level across your back for every reading. The calculator averages the three bust numbers, so one slightly-off reading won’t break your result.
US / UK / EU size conversion
Cup letters diverge above D between systems. A few equivalents:
| US | UK | EU cup |
|---|---|---|
| DD | DD | E |
| DDD | E | E |
| G (US) | F | F |
| H (US) | FF | G |
| I (US) | G | G |
| J (US) | GG | H |
Band sizes: US/UK use inches (30, 32, 34…); EU uses centimeters (65, 70, 75, 80…).
Frequently asked questions
Why six measurements instead of two?
Two measurements assume every body distributes volume the same way — they don’t. Three underbust readings capture how firm your ribcage is (which sets the band), and three bust readings capture volume from different angles (which sets the cup). The average is far more reliable than any single reading.
Which measurement matters most for band size?
The snug underbust. Your band should feel like that reading — firm and level. The loose and tight readings tell the calculator how much “give” your ribcage has, which refines the recommendation.
Why does the leaning bust measurement matter?
Standing compresses tissue against the chest; leaning lets it project naturally. If your leaning number is much larger than standing, you likely have a projected shape — and the calculator will flag it, because molded cups tend to gap on projected shapes while seamed, unlined styles fit better.
What are sister sizes?
Sister sizes share the same cup volume with a different band — for example, 34E, 36DD, and 32F (UK) all hold roughly the same amount. If your calculated band feels tight but the cups fit, try the sister size with a bigger band; if the band rides up, try the smaller band.
Do US, UK, and EU bra sizes differ?
Yes — above a D cup the letters diverge. US goes D, DD, DDD, G, H while UK goes D, DD, E, F, FF, G. EU bands are in centimeters (75, 80, 85) with its own cup letters. Use the sizing-system toggle above and the conversion table to translate.
How often should I re-measure?
Every 6–12 months, or after significant weight changes, pregnancy, or starting a new workout routine. Band elasticity wears out too — a bra that fit a year ago may not anymore.
Why does my band ride up in the back?
A riding band almost always means the band is too big — it’s doing none of the support work. Try your sister size with a smaller band and a larger cup (for example, 36DD → 34E in UK sizing).