Bra Size Calculator + Sister Sizes

Quick answer: measure snugly around your ribcage just under your bust (the underbust) and loosely around the fullest part (the bust). The modern method: round the underbust up to an even number for the band, then every inch of bust over the band is one cup: 1 A, 2 B, 3 C, 4 D, 5 DD. A 32-inch underbust and a 37-inch bust is a 32DD. Makers that add 4 inches to the band would call it 36A.

How to use it

Measure in a bra without padding, the tape level all the way round. Type your underbust and bust in inches or centimetres. The answer is your starting size by the modern method in US, UK and EU letters, then what five makers’ own charts make of the same numbers, your sister sizes, and the size to try if the band or cups do not fit when you try it on. It is a starting size: check the brand’s own chart, and our women’s size converter for your clothes.

Why calculators give you different sizes

Most makers count about one cup per inch of bust over the band. The band is where they differ. Triumph UK uses the underbust itself: “If the number is even, that is your band size. If it is odd, round up to the next even number.” Vanity Fair adds inches: “If your underbust measurement is an even number, add 4 to get your band size.” Wacoal’s and ThirdLove’s calculators use their own tables (ThirdLove’s band is about 2 inches over the underbust; Wacoal’s adds up to 4 inches on a small underbust and less on a larger one), and Triumph’s own EU chart reads a 78–82 cm underbust as an 80 band (a US 36). Triumph UK on the old way: “The result is a band that is too loose and a cup letter that looks smaller on the label but provides less support in practice.” That is why the headline here is the modern method: our choice.

Cup letters: US, UK and EU

US and UK cups match up to DD; then the UK goes E, F, FF, G, GG and the US DDD, G, H, I (Wacoal’s size charts). EU cups run one letter per step, so a UK DD is an EU E (Fantasie’s international size guide). EU bands are centimetres: a 32 band is EU 70 and FR 85.

Sister sizes

One band down and one cup up holds the same cup volume: “a 34C has the same cup volume as a 32D or 36B because the cup works in relation to the band it sits on” (M&S); ThirdLove’s chart puts 36C, 38B and 40A in one row for the same reason. Try a sister size when the cups fit and the band does not.

Three worked examples

Underbust 32 in, bust 37 in: 32DD by the modern method (UK 32DD, EU 70E). Wacoal and Vanity Fair say 36A, ThirdLove 34B½: on a 32 band those are a 32C and a 32C½, smaller cups than a 32DD.

Underbust 33 in, bust 38 in: 34D (the 33 rounds up to 34). Wacoal says 36B, the same cup volume as a 34C; Vanity Fair’s chart has no size, because its 38 band leaves no inch for a cup.

Underbust 86 cm, bust 104 cm: 34G in US letters, a UK 34F and an EU 75G. Triumph’s EU chart says 85D, the same cup volume as a 34DDD.

When you try it on

• The band rides up at the back: one band down, one cup up. “If it rides up your back, the band is too loose. Go down a size” (Triumph).
• The band digs in: “First, try a looser setting. Then try a bigger band with a cup size smaller (sister size)” (Lane Bryant).
• The cups gape or wrinkle: one cup down. You spill over the top or sides, or the centre lifts off your chest: one cup up.
• The straps dig in: Triumph and ThirdLove say the band is too big (one band down, one cup up); Lane Bryant says loosen the straps or go up a cup.

Common mistakes

• Measuring over a padded bra. The padding adds inches to the bust and cups you do not need.
• A loose tape under the bust. The band measurement is snug; the bust measurement is not.
• Comparing sizes across brands by the letter. A 36A and a 32DD are not neighbours: the band changes what a letter means. Compare on the same band with sister sizes.
• Treating any calculator as the last word. Brands cut differently; the size here is where to start trying on.

More on Needle Style

Outfits for broad shoulders and a large bust, halter neck dresses, corset top outfits, hairstyles for a strapless dress and hairstyles for a one-shoulder dress. Our body shape calculator uses the same bust measurement.

Methods from Triumph (UK and EU), ThirdLove’s and Wacoal’s calculators and Vanity Fair; cup letters from Wacoal and Fantasie; sister sizes and fit fixes from M&S, Lane Bryant, Triumph and ThirdLove. Checked 2026-09-28.

FAQ