Bra Sizes - Calculating Cup Volume and Breast Weight

Calculating Cup Volume and Breast Weight

The average breast weighs about 0.5 kilograms (1.1 lb). Each breast contributes to about 4–5% of the body fat.

The density of fatty tissue is more or less equal to 0.9 kg/l for all women. The volume of a woman's individual breasts can vary. Bra designers can give it the shape of a hemisphere or an hemi-spheroid by fitting it into a cup. If the bust is considered essentially a half-sphere, its volume V is determined by the following formula:

where D is the diameter of the sphere, and r is its radius.

If the breast is shaped more like a spheroid, the designer might use a formula like the following:

where Db equals diameter of the hemi-spheroid's base and h equals the height of the spheroid. Other formulas can be derived as needed to design bras for differently shaped breasts. All of these formulas assume that the breasts conform to the mentioned mathematical model.

Cups give a hemi-sperical shape to breasts and underwires give shape to cups. So the curvature radius of the underwire is the key parameter to determine volume and weight of the breast. The same underwires are used for the cups of sizes 36A, 34B, 32C, 30D and etc... so those cups have the same volume. The reference numbers of underwire sizes are based on a B cup bra, for example underwire size 32 is for 32B cup (and 34A, 30C...). An underwire size 30 width has a curvature diameter of 3-inch 5/6 ≈ 9.7 cm and this diameter increases by ⅓ inch ≈ 0.847 cm by size. The table below shows volume calculations for some cups that can be found in a ready-to-wear large size shop.