Fitness Tools | Body Composition Equations
Durnin-Womersley (1974)
Section titled “Durnin-Womersley (1974)”Sites (4): Triceps, biceps, subscapular, suprailiac
Appropriate use: General population, all ages. Most widely validated across diverse populations.
Method: Calculates body density from the log of the sum of four skinfolds, using age- and sex-specific coefficients. Body density is then converted to body fat percentage using a secondary equation (typically Siri).
Density formula: D = C - (M * log10(sum_of_4_skinfolds))
where C and M are age- and sex-specific constants.
Age brackets (male):
| Age | C | M |
|---|---|---|
| < 17 | 1.1533 | 0.0643 |
| 17-19 | 1.1620 | 0.0630 |
| 20-29 | 1.1631 | 0.0632 |
| 30-39 | 1.1422 | 0.0544 |
| 40-49 | 1.1620 | 0.0700 |
| 50+ | 1.1715 | 0.0779 |
Age brackets (female):
| Age | C | M |
|---|---|---|
| < 17 | 1.1369 | 0.0598 |
| 17-19 | 1.1549 | 0.0678 |
| 20-29 | 1.1599 | 0.0717 |
| 30-39 | 1.1423 | 0.0632 |
| 40-49 | 1.1333 | 0.0612 |
| 50+ | 1.1339 | 0.0645 |
Jackson-Pollock 7-Site (1978)
Section titled “Jackson-Pollock 7-Site (1978)”Sites (7): Chest, axilla, tricep, subscapular, abdominal, suprailiac, thigh
Appropriate use: Most comprehensive assessment. Best for trained individuals and research settings where maximum accuracy is needed.
Method: Uses sum of 7 skinfolds with quadratic and age terms.
Male: D = 1.112 - (0.00043499 * S) + (0.00000055 * S²) - (0.00028826 * age)
Female: D = 1.097 - (0.00046971 * S) + (0.00000056 * S²) - (0.00012828 * age)
where S = sum of 7 skinfolds (mm).
Jackson-Pollock 4-Site
Section titled “Jackson-Pollock 4-Site”Sites (4): Abdominal, triceps, thigh, suprailiac
Appropriate use: Simplified alternative when 7-site measurement is impractical. Directly calculates body fat percentage (no intermediate density step).
Male: BF% = (0.29288 * S) - (0.0005 * S²) + (0.15845 * age) - 5.76377
Female: BF% = (0.29669 * S) - (0.00043 * S²) + (0.02963 * age) + 1.4072
where S = sum of 4 skinfolds (mm).
Jackson-Pollock 3-Site (1985)
Section titled “Jackson-Pollock 3-Site (1985)”Sites (3): Chest, triceps, subscapular (male) OR triceps, thigh, suprailiac (female)
Appropriate use: Quick assessment when fewer measurement sites are available. Sex-specific site selection.
Male: D = 1.10938 - (0.0008267 * S) + (0.0000055 * S²) - (0.000244 * age)
Female: D = 1.0994921 - (0.0009929 * S) + (0.0000023 * S²) - (0.0001392 * age)
where S = sum of 3 skinfolds (mm).
Density-to-Body-Fat Conversion Equations
Section titled “Density-to-Body-Fat Conversion Equations”All take body density (g/cm³) as input and return body fat percentage.
| Equation | Formula | Best For |
|---|---|---|
| Siri (1961) | (495 / D) - 450 | General population (default) |
| Brozek (1963) | (457 / D) - 414.2 | General population |
| Schutte (1984) | (437.4 / D) - 392.8 | Black males |
| Wagner (1996) | (486 / D) - 439 | Black females |
| Ortiz (1992) | (483.2 / D) - 436.9 | Hispanic populations |
Note: Siri is the most commonly used default. Population-specific equations (Schutte, Wagner, Ortiz) may provide better accuracy for specific demographics.