Bra Sizing Guide: Measure Your Size at Home
Your correct bra size is two numbers — a band measurement and the difference between band and bust — and you can find both with a tape measure and five minutes.
Most bra fit problems come down to one thing: the size on the tag was estimated once, years ago, and never re-checked. Bra size changes with weight fluctuations, pregnancy, and even the specific bra's cut, so it's worth re-measuring every so often with a soft tape measure. This guide covers how to measure your band and bust at home, how to turn that into a cup letter, and how sister sizing lets you fine-tune fit without buying a whole new size.
Size chart
Subtract your band measurement from your bust measurement to get a number in inches, then match that difference to a cup letter below. Your band size is your band measurement (rounded to the nearest even number, minus a small allowance — see the FAQ for how brands vary on this).
| Bust Minus Band (in) | Cup Size |
|---|---|
| 0–1 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD / E |
| 6 | DDD / F |
| 7 | G |
How to measure yourself at home
- Use a soft fabric tape measure, not a rigid one, and measure in a well-fitting (or no) bra, standing straight.
- Band measurement: wrap the tape snugly around your ribcage directly under your bust, keeping it level and parallel to the floor.
- Bust measurement: wrap the tape around the fullest part of your bust, usually across the nipple line, without pulling it tight.
- Round both measurements to the nearest whole number, then subtract band from bust to get your cup difference.
Sister sizing explained
- A 'sister size' has the same cup volume as your size but in a different band — going up one band size and down one cup letter (or vice versa) keeps roughly the same volume.
- Example: if a 34C feels too tight in the band but the cup fits well, a 36B has essentially the same cup volume with a looser band.
- Sister sizing is useful when a specific bra runs small or large in the band, or when you want more hook-and-eye adjustment room as you break in a new bra.
Common bra fit mistakes
- Wearing the band too loose: the band should feel snug on the loosest hook when new, since bands stretch out over time — most of a bra's support comes from the band, not the straps.
- Cup too small, showing as bulging at the top or sides ('quad-boob'), or too large, showing as loose fabric or gapping at the top of the cup.
- Assuming size is fixed across brands and styles — cup and band can both shift by a size or more between brands, so treat any chart as a starting point and try before committing.
- Not re-measuring after weight changes, pregnancy, or breastfeeding, all of which commonly shift both band and cup size.
Shop bras and a soft measuring tape on Amazon
Once you know your size, here's where to find it.
Shop bras and a soft measuring tape on AmazonAs an Amazon Associate we may earn from qualifying purchases.
Frequently asked questions
Measure your band (snug, directly under the bust) and your bust (at the fullest point), both in inches. Subtract band from bust — that difference in inches corresponds to a cup letter (roughly 1 inch = A, 2 inches = B, and so on). Your band number plus that cup letter is your estimated size, though brands vary slightly in how they round the band number.
More size guides
- Pants and Jeans Sizing Guide
A size 32 waist means something different at nearly every brand — here's how to measure yourself once and stop guessing at the fitting room.
- Ring Size Chart & Sizing Guide
A strip of paper, a ruler, and five minutes gets you a genuinely usable ring size — no trip to the jeweller required for a first estimate.
- Shoe Size Chart & Conversion Guide
US, UK, and EU shoe sizes don't line up the way most conversion apps suggest — foot length in cm is the one number that actually travels between systems.
- Ski Boot Size Chart & Sizing Guide
Ski boots use Mondopoint sizing — foot length in cm — not your regular shoe size, and they're supposed to fit snugger than you'd expect from any other footwear.
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