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.
| Underwire size | Bra size (US system) | Cup diameter | Volume of one cup | Weight of both breasts |
|---|---|---|---|---|
| 30 | 32A 30B 28C | 9.7 cm (3 in 5/6) | 240 cc (0.51 US pt) | 0.43 kg (0.95 lb) |
| 32 | 34A 32B 30C 28D | 10.6 cm (4 in 1/6) | 310 cc (0.66 US pt) | 0.56 kg (1.2 lb) |
| 34 | 36A 34B 32C 30D 28E | 11.4 cm (4 in 1/2) | 390 cc (0.82 US pt) | 0.70 kg (1.5 lb) |
| 36 | 38A 36B 34C 32D 30E 28F | 12.3 cm (4 in 5/6) | 480 cc (1.0 US pt) | 0.86 kg (1.9 lb) |
| 38 | 40A 38B 36C 34D 32E 30F 28G | 13.1 cm (5 in 1/6) | 590 cc (1.2 US pt) | 1.1 kg (2.4 lb) |
| 40 | 42A 40B 38C 36D 34E 32F 30G 28H | 14.0 cm (5 in 1/2) | 710 cc (1.5 US pt) | 1.3 kg (2.9 lb) |
| 42 | 44A 42B 40C 38D 36E 34F 32G 30H 28I | 14.8 cm (5 in 5/6) | 850 cc (1.8 US pt) | 1.5 kg (3.3 lb) |
| 44 | 46A 44B 42C 40D 38E 36F 34G 32H 30I 28J | 15.7 cm (6 in 1/6) | 1,000 cc (2.1 US pt) | 1.8 kg (4.0 lb) |
| 46 | 48A 46B 44C 42D 40E 38F 36G 34H 32I 30J 28K | 16.5 cm (6 in 1/2) | 1,180 cc (2.5 US pt) | 2.1 kg (4.6 lb) |
| 48 | 50A 48B 46C 44D 42E 40F 38G 36H 34I 32J 30K 28L | 17.4 cm (6 in 5/6) | 1,370 cc (2.9 US pt) | 2.5 kg (5.5 lb) |
| 50 | 52A 50B 48C 46D 44E 42F 40G 38H 36I 34J 32K 30L 28M | 18.2 cm (7 in 1/6) | 1,580 cc (3.3 US pt) | 2.8 kg (6.2 lb) |
| 52 | 54A 52B 50C 48D 46E 44F 42G 40H 38I 36J 34K 32L 30M 28N | 19.0 cm (7 in 1/2) | 1,810 cc (3.8 US pt) | 3.3 kg (7.3 lb) |
| 54 | 56A 54B 52C 50D 48E 46F 44G 42H 40I 38J 36K 34L 32M 30N 28O | 19.9 cm (7 in 5/6) | 2,060 cc (4.4 US pt) | 3.7 kg (8.2 lb) |
| 56 | 58A 56B 54C 52D 50E 48F 46G 44H 42I 40J 38K 36L 34M 32N 30O 28P | 20.7 cm (8 in 1/6) | 2,340 cc (4.9 US pt) | 4.2 kg (9.3 lb) |
| 58 | 60A 58B 56C 54D 52E 50F 48G 46H 44I 42J 40K 38L 36M 34N 32O 30P 28Q | 21.6 cm (8 in 1/2) | 2,640 cc (5.6 US pt) | 4.8 kg (11 lb) |
| 60 | 60B 58C 56D 54E 52F 50G 48H 46I 44J 42K 40L 38M 36N 34O 32P 30Q 28R | 22.4 cm (8 in 5/6) | 3,000 cc (6.3 US pt) | 5.3 kg (12 lb) |
Read more about this topic: Bra Sizes
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