Body fat calculator.
Estimate your body fat percentage using circumference or skinfold measurements. Choose a method, enter your measurements, and see your result.
Enter measurements
Choose a method, then enter the measurements it requires.
Estimated body fat
This is an estimate based on your measurements, not a diagnosis or a direct measurement of body fat.
- Intermediate body density
- 1.052863 g/cm³
- Estimated fat mass
- —
- Estimated fat-free mass
- —
Fat mass and fat-free mass cannot be calculated from this outlier estimate. Verify the measurements, units, site placement, and suitability of the selected equation.
The raw estimate is below 2% or above 70%. It has not been clamped; verify units, site placement, and whether the source equation fits the person measured.
Method note
Developed in U.S. Navy personnel. Circumference placement and tape tension can materially change the estimate.
How to measure
Repeatability matters more than apparent precision. Measure circumferences with a snug, level tape that does not compress the skin. Take each circumference at least twice and use the average when readings differ.
Navy circumference sites
- Height: barefoot and standing upright.
- Neck: just below the larynx, with the tape sloping slightly downward toward the front.
- Male abdomen: horizontally at the navel after a normal exhalation, without pulling in.
- Female waist: horizontally at minimum abdominal width.
- Female hip: the largest horizontal circumference around the buttocks.
Skinfold technique
- Measure on the right side and pinch skin plus subcutaneous tissue, not muscle.
- Place the caliper about 1 cm below the fingers holding the fold.
- Take at least two readings per site while rotating through sites.
- If readings differ by more than 2 mm, repeat and use the closest two.
- Record millimetres, not centimetres.
Caliper technique is a major source of error
Consistent placement is essential. These field instructions support repeatability; they do not make untrained self-measurement equivalent to professional anthropometry.
Equations and source ranges
Circumferences use centimetres, skinfold sums use millimetres, age uses completed years, and density is expressed in g/cm³. Full precision is retained until display.
Technical military report
U.S. Navy circumference
Male density = 1.0324 − 0.19077 log₁₀(waist at navel − neck) + 0.15456 log₁₀(height)
Female density = 1.29579 − 0.35004 log₁₀(waist + hip − neck) + 0.22100 log₁₀(height)
The male report studied 602 U.S. Navy men aged 18–56 and reported a standard error equivalent to about 3.52 body-fat percentage points; an independent sample of 100 produced about 2.70 points. The female report studied 214 U.S. Navy women aged 18–44. Military samples should not be treated as universally accurate.
Peer-reviewed derivation study
Jackson–Pollock three-site
Male S = chest + abdomen + thigh
Density = 1.10938 − 0.0008267S + 0.0000016S² − 0.0002574(age)
Female S = triceps + suprailiac + thigh
Density = 1.0994921 − 0.0009929S + 0.0000023S² − 0.0001392(age)
Source range: men aged 18–61 and women aged 18–55.
Practical review / field equation
Jackson–Pollock four-site
S = triceps + abdomen + suprailiac + thigh
Male body fat % = 0.29288S − 0.0005S² + 0.15845(age) − 5.76377
Female body fat % = 0.29669S − 0.00043S² + 0.02963(age) + 1.4072
This equation returns body-fat percentage directly and is not passed through Siri. Its source is a practical review/field-assessment article, not a new broad independent validation cohort, so it is not presented as more accurate than the three- or seven-site methods. The calculator applies the adult Jackson–Pollock ranges of 18–61 for men and 18–55 for women. For coefficient verification, the open-access methods section of Maalin et al. (2021) reproduces both equations exactly and attributes them to Jackson & Pollock (1985).
Peer-reviewed derivation study
Jackson–Pollock seven-site
S = chest + midaxillary + triceps + subscapular + abdomen + suprailiac + thigh
Male density = 1.112 − 0.00043499S + 0.00000055S² − 0.00028826(age)
Female density = 1.097 − 0.00046971S + 0.00000056S² − 0.00012828(age)
Source range: men aged 18–61 and women aged 18–55.
Peer-reviewed derivation study
Durnin–Womersley four-site
S = biceps + triceps + subscapular + suprailiac · L = log₁₀(S) · Density = intercept − slope × L
The study included 209 men and 272 women aged 16–72. The published age bands select fixed coefficients; the calculator does not interpolate between them.
| Age | Intercept | Slope |
|---|---|---|
| 16 | 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 |
| 50–72 | 1.1715 | 0.0779 |
| Age | Intercept | Slope |
|---|---|---|
| 16 | 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 |
| 50–72 | 1.1339 | 0.0645 |
Book chapter / conversion model
Siri density conversion
Body fat % = 495 ÷ body density − 450
Navy, Jackson–Pollock three- and seven-site, and Durnin–Womersley first estimate body density. Siri then applies a two-compartment model with assumptions about the densities of fat mass and fat-free mass. It does not directly measure either compartment.
Static worked examples
These examples remain available when JavaScript is disabled and show the calculator’s display rounding.
Navy male example
Height 178 cm, waist at navel 90 cm, and neck 38 cm produce an intermediate density of 1.052863 g/cm³ and an estimated body fat of 20.1%.
Durnin–Womersley female example
Age 35 with biceps 10 mm, triceps 18 mm, subscapular 16 mm, and suprailiac 20 mm produces an intermediate density of 1.028149 g/cm³ and an estimated body fat of 31.4%.
Why methods disagree
Each equation is a population regression using different sites, samples, and assumptions. Fat distribution, muscularity, ethnicity, training status, age, equation sex, tape placement, caliper pressure, and operator technique can affect prediction behaviour.
A difference between two methods is not proof that body fat changed. Do not average methods or treat their outputs as interchangeable measurements. For trends, keep the method, sites, equipment, operator, and measurement conditions consistent.
Limitations and interpretation
- The equations estimate body density or body fat from population regressions; they do not directly measure fat tissue.
- The Navy equations were developed in military personnel. The Jackson–Pollock and Durnin–Womersley equations came from specific adult samples and age ranges.
- Hydrostatic weighing and Siri’s two-compartment conversion introduce their own assumptions about fat mass and fat-free mass.
- Skinfold self-measurement can be substantially less repeatable than measurement by a trained operator.
- No result is a diagnosis, accuracy guarantee, body-fat classification, “ideal” value, target weight, or advice to change body weight.
Original sources
- Peer-reviewed derivation studies Jackson, A. S., & Pollock, M. L. (1978). Generalized equations for predicting body density of men. British Journal of Nutrition, 40(3), 497–504. DOI PubMed Jackson, A. S., Pollock, M. L., & Ward, A. (1980). Generalized equations for predicting body density of women. Medicine & Science in Sports & Exercise, 12(3), 175–181. DOI PubMed
- Practical review / field equation Jackson, A. S., & Pollock, M. L. (1985). Practical Assessment of Body Composition. The Physician and Sportsmedicine, 13(5), 76–90. DOI PubMed Open-access coefficient cross-check Maalin, N., Mohamed, S., Kramer, R. S. S., Cornelissen, P. L., Martin, D., & Tovée, M. J. (2021). Beyond BMI for self-estimates of body size and shape: A new method for developing stimuli correctly calibrated for body composition. Behavior Research Methods, 53, 1308–1321. The methods section explicitly reproduces the male and female four-site equations. DOI Open-access full text
- Peer-reviewed derivation study Durnin, J. V. G. A., & Womersley, J. (1974). Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. British Journal of Nutrition, 32(1), 77–97. DOI Publisher page
- Book chapter / conversion model Siri, W. E. (1961). Body Composition from Fluid Spaces and Density: Analysis of Methods. In J. Brožek & A. Henschel (Eds.), Techniques for Measuring Body Composition (pp. 223–244). National Academy of Sciences–National Research Council. National Academies volume Online volume Later reprint record