Bra Sizes and How to Measure
A bra size is a band number from your underbust plus a cup letter from the bust-to-band gap, but brands convert differently, so use each brand's own chart.
By Elliana SmithContributing writer.
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The short answer
A bra size like 34C has two parts:
- The band number (34) comes from the measurement around your ribcage, just under the bust.
- The cup letter (C) comes from how much larger your bust measurement is than the band.
There is no single standard. Brands turn the same tape readings into different sizes, so measure once, then check the size chart of the brand you are buying.
How to measure
You need a soft tape measure in inches.
- Underbust: wrap the tape snugly around your ribcage directly under the bust. Keep it level all the way around, not riding up in the back.
- Bust: wrap the tape around the fullest part of the bust, level and snug but not squeezing.
- Write down both numbers.
Finding your band size
Three methods are in common use:
| Method | How it works | Example: 31 in underbust |
|---|---|---|
| Measured band | Round the underbust to the nearest even number | 30 or 32 |
| Plus four | Add 4 if the number is even, 5 if it is odd | 36 |
| Brand chart | The brand maps a range of underbust readings to each band | ThirdLove: 34 |
The plus-four method applies mainly to US and UK sizes. Many stores now use their own chart or calculator, and those charts vary between makers. ThirdLove, for example, puts underbust readings above 30.5 inches and up to 32.5 inches in a 34 band.
Finding your cup size
Subtract the band from the bust measurement. In the common US chart each inch of difference is one cup letter:
| Bust minus band | Cup |
|---|---|
| Under 1 in | AA |
| 1 in | A |
| 2 in | B |
| 3 in | C |
| 4 in | D |
| 5 in | DD or E |
| 6 in | DDD or F |
Past D, US labels are not consistent. Some brands run D, DD, DDD, DDDD, then E; others use D1, D2 and D3; many go from DDD straight to G and H. That makes larger cups hard to compare between makers. UK brands follow AA, A, B, C, D, DD, E, F, FF, G and onward, one inch apart.
Brand charts also differ here. ThirdLove's chart measures the cup against your underbust rather than the rounded band, so its numbers do not match the table above even for the same person.
Sister sizes
Cup volume depends on the band. A 30D, 32C, 34B and 36A have the same cup volume, and these are called sister sizes. If a band rides up in the back while the cups fit, ThirdLove suggests going down one band and up one cup, for example from 34C to 32D.
Tips for a good fit
- Try the size each brand's chart gives you; your size can change from brand to brand and style to style.
- The band should sit level around your body.
- Measure again when your body changes, since the numbers that set your size change with it.
How we count
On October 27, 2026, Wiki Shopping listed 172 bras in clothing, shoes and jewelry: 55 in black and 33 listed as everyday bras. Counts come from store listings and change as listings are added or removed.