Brassiere Sizing

Brassiere sizes take the form “34B,” where the number is the band size (also called frame size) and the letter is the cup size. According to the market research firm NPD, the most popular bra size in the United States went from 34B to 36B in 1991, and from 36B to 36C in 2000.

There is no way of determining with a tape measure what bra size a woman needs. The only way of determining whether a bra fits is to try it on. Nevertheless, a tape measure can be used to get an approximation to the size as a starting point for fittings. It isn't possible to do a good job of measuring yourself, because you won't be able to keep the tape level and because your arms will not be relaxed at your sides. Get a friend to help.

You need to measure three things, all with the tape horizontal:

• • the distance around the rib cage just below the bust

  • the distance around the fullest part of the bust (generally, over the nipples), wearing a light, unpadded bra that fits well

  • the distance around the chest under the arms but above the bust

Band size

The band size is based on the circumference of the rib cage below the breasts. In North America the measurement is made in inches, and numbers in the thirties and forties are common. Elsewhere the numbers are much larger (e.g., “85”) reflecting measurements made in centimeters.

U.S. band size

To find U.S. band size, measure around the rib cage just below the bust, in inches. Keep the tape quite tight and level. Round up to the nearest whole inch. Add 5, unless the measurement is over 33 inches, in which case add 3. If the result is an odd number, add an additional 1.

The band size is slightly adjustable, since most bras close with hooks on the band, usually with three possible positions. Usually sizes 36D and 38C and larger have 3 hooks vertically, across the band, to provide more support; other sizes have only 2.

ISO band size

Measure around the rib cage just below the bust in centimeters. Round up to the nearest whole number.

Converting between US and ISO band sizes

In finding the metric equivalent of a U.S. size, it is best not to begin with a U.S. bra size, but with the measurement of the rib cage just below the bust. Instead of rounding up to the nearest whole inch, round up to the nearest half inch.

Due to the difference in the sizes of the centimeter and inch, and the “round up” method, the ranges have a maximum unavoidable error of 0.2 inch. Girths not shown should try both sizes, that is: 36½, try 90 and 95; 40½, try 100 and 105; 44½, try 110 and 115.

To find a U.S. band size from a measured rib cage girth in centimeters, rounded up to the nearest whole centimeter.

Older systems

Cup size

U.S. cup sizes

Realize that in the U.S. "system" cup size is relative to band size. Within a single line of a single maker, the B cup of a bra with a 38 inch band is bigger than a B cup with a 34 inch band.

To find cup size, measure around the fullest part of the bust while wearing an unpadded bra that fits well, again in inches. Subtract the band size. The difference is given in the first column below.

Measure under the arms, but above the breasts. Some designs assume this figure it will be the same as the band size, but it often is not. Subtract this number from the full bust measurement. See column 2 of the table below.

The table is an approximation compiled from manufacturers' catalogs. Bra sizing is a nightmare, especially in the larger sizes, where a wealth of differing letter codes are in use. Apparently most manufacturers assume an inch difference between cup sizes, but many do not. Some use an inch and a half, or even two inches. Certain manufacturers do not even keep a consistent difference between cup sizes. So, try it on.