What Is Bust Size?

In sizing, the bust is the circumference of the torso at the fullest part of the breasts, measured with the tape level around the body, usually at nipple height. It is a body measurement, taken in inches in the US and UK and in centimeters everywhere else, and it means the same thing on a bra chart, a dress chart and a dressmaker’s pattern. "Bust size" and "bust measurement" are the same number.

The word is older than the measurement. "Bust" came into English from the Italian busto, a sculpture of head and shoulders, and by the nineteenth century meant the upper body of a woman as a dressmaker measured it. Sizing kept the word because it names the one circumference that distinguishes a bodice from a shirt. In everyday speech it drifts: people say bust for the breasts themselves, or for a bra size ("a 34DD bust"), and neither is the sizing meaning. On this site bust always means the tape at the fullest point.

The cup letter is the bust minus the band, at one inch per letter: a bust one inch over the band is an A, two is a B, three a C, four a D, five a DD, six a DDD, seven a G, eight an H. The bust measurement sets the ceiling of that sum and the band sets the floor, which is why the same bust can be almost any cup. A 38-inch bust is a 36B on a 36 band, a 34D on a 34, a 32DDD on a 32 and a 30H on a 30: one number, four sizes, and every one of them describes a different breast on a different ribcage.

Two consequences follow. First, "bust size" is not a euphemism for cup size, though it is used as one; a 40-inch bust can be small-breasted on a wide ribcage or full-breasted on a narrow one. Second, a bust measurement is only useful when the band is measured with it, and it must be measured the same way every time: level, at the fullest point, relaxed, over an unpadded bra, because a padded bra adds an inch and a compressing tape removes one, and each inch is a cup letter. The how bra sizes work page has the full walkthrough; the chart with pictures draws every combination.

Enter both measurements and the tool returns the size, the sister sizes and the label in five systems. Change the underbust and watch the same bust move through the cups.

The full calculator adds the sister sizes, the size page and the brand run; this tool is the arithmetic only.

Clothing charts use the bust alone, because a dress does not have a band. A US women’s size chart runs roughly bust 32 to 33 inches at size 2, 34 to 35 at size 6, 36 to 37 at size 10, 38 to 40 at size 14 and 42 to 44 at size 18, with every brand drawing its own lines; UK sizes are the US number plus four. The chart is honest as far as it goes, and it goes no further than the bust: two people with a 38-inch bust and 30 and 36-inch underbusts are the same dress size and five bra sizes apart, and the one with the small ribcage will find the dress fits at the bust and floats at the waist.

That is why fitted clothing and bras are sized differently and why the bust measurement matters for both. For a top, it is the size. For a bra, it is half the size, and the half that only means something once the ribcage under it is measured too. The alpha size converter maps S to XL to bra sizes for the garments that split the difference.