Enter the skinfold measurements of the biceps, triceps, subscapular, and suprailiac into the calculator to determine the body density (you may enter values in mm, cm, or inches using the unit selectors).
Disclaimer: Results are estimates for educational use only and not medical advice. The equations are intended for ages 16+ and may be inaccurate for some individuals; if you’re under 16, pregnant, or have a medical condition or eating disorder history, consult a qualified clinician.
Accuracy & limitations
SkinfoId-based estimates depend heavily on caliper quality, correct site location, and consistent technique—small measurement errors can materially change results. The Siri and Brozek equations use two-compartment assumptions about fat-free mass density and hydration, so accuracy may be reduced for very lean or very muscular individuals, older adults, and some medical conditions.
References (formulas used)
- Durnin JVGA, Womersley J. (1974). Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged 16–72 years. British Journal of Nutrition.
- Siri WE. Two-compartment model relating body density to body fat percentage (commonly cited in body composition texts).
- Brozek J, et al. Alternative two-compartment equation relating body density to body fat percentage (commonly cited in body composition texts).
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Body Density Formula
The following formula is used to calculate body density.
D = 1.1422 − 0.0544·log₁₀(Σ skinfolds),
- Where D is the body density (g/cm³)
- Σ skinfolds is the sum of the biceps + triceps + subscapular + suprailiac skinfolds (with the sum in mm)
This equation is used for males age 30–39. The following table displays the formulas for males and females by age group. In the formulas below, log₁₀(s) = log₁₀(skinfold sum of the 4 measurements in mm).
| Age | Men | Women |
| 16–19 | D = 1.1620 – (0.0630 * log₁₀(s)) | D = 1.1549 – (0.0678 * log₁₀(s)) |
| 20–29 | D = 1.1631 – (0.0632 * log₁₀(s)) | D = 1.1599 – (0.0717 * log₁₀(s)) |
| 30–39 | D = 1.1422 – (0.0544 * log₁₀(s)) | D = 1.1423 – (0.0632 * log₁₀(s)) |
| 40–49 | D = 1.1620 – (0.0700 * log₁₀(s)) | D = 1.1333 – (0.0612 * log₁₀(s)) |
| 50+ | D = 1.1715 – (0.0779 * log₁₀(s)) | D = 1.1339 – (0.0645 * log₁₀(s)) |
Body Density Definition
What is a body density? Body density is defined as total mass per unit volume of an individual human. It’s often estimated using a formula like the one above, which takes skinfold measurements throughout the body.
Example Problem
How to calculate body density?
- First, take the measurements of the skinfold in each of the 4 areas.
For this example, we find measurements as follows: 2mm, 3mm, 5mm, 2mm, for the biceps, triceps, subscapular, and suprailiac respectively.
- Next, sum the skinfold measurements.
Adding the measurements together we get a sum of 12mm.
- Finally, calculate the body density.
Calculate the body density using the formula above. D = 1.1422 – (0.0544 * log₁₀(12)) = 1.084 g/cm^3.
About Body Density
How can body density be used to calculate body fat %? Using the Siri equation, an estimate of body fat percentage can be calculated from body density: body fat % = (495 / D) − 450, where D is in g/cm³. (Another commonly used equation is Brozek: body fat % = (457 / D) − 414.2.)
What are skinfolds? Skinfolds are measurements of a pinched fold of skin and subcutaneous fat taken with calipers at specific anatomical sites to help estimate body fat percentage.
