Skinfold Body Fat Calculator

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Walk-through

How to Use This Calculator

3 steps

1

Enter your sex, age, and bodyweight

Select male or female — the Jackson-Pollock formula uses different regression coefficients and skinfold sites for each — and enter your age. Bodyweight is optional and only needed for the Fat & Lean Mass tab.

2

Pick 3-Site or 7-Site and enter your skinfold measurements

Using skinfold calipers, measure each site in millimeters (taking 2-3 readings per site and averaging them is recommended), then enter the values. The 3-Site tab uses fewer sites for a quicker estimate; the 7-Site tab uses all seven sites for a more precise one.

3

Read your body fat % and category

The result card shows your estimated body fat percentage, body density, and which sex-specific category it falls into. Switch to the Fat & Lean Mass tab to see the fat and lean mass split from your most recently completed method.

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Reference

Formula & Methodology

3 formulas

Body density — 3-site (Jackson & Pollock, 1978/1980)

Men (chest+abdomen+thigh): BD = 1.10938 - 0.0008267xS + 0.0000016xS^2 - 0.0002574xAge. Women (triceps+suprailiac+thigh): BD = 1.0994921 - 0.0009929xS + 0.0000023xS^2 - 0.0001392xAge

S is the sum of the 3 skinfold measurements in millimeters. The men's equation is from Jackson & Pollock (1978); the women's equation, which uses a different site set, is from Jackson, Pollock & Ward (1980).

Body density — 7-site (Jackson & Pollock, 1978/1980)

Men: BD = 1.112 - 0.00043499xS + 0.00000055xS^2 - 0.00028826xAge. Women: BD = 1.097 - 0.00046971xS + 0.00000056xS^2 - 0.00012828xAge

S is the sum of all 7 skinfold measurements in millimeters (chest, axilla, triceps, subscapular, abdominal, suprailiac, thigh — the same seven sites for both sexes). Using more sites generally improves precision over the 3-site equation.

Body density to body fat % — the Siri equation

%Body Fat = 495 / Body Density - 450

Published by William Siri in 1961, this equation converts body density (grams per cubic centimeter) into an estimated percentage of body fat, based on the assumed densities of fat versus fat-free body tissue.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Team · Updated 2026-07-23 · 3 sources

Editorial accountability

Author: Calculover Editorial Team - Health content editors

Owner: Calculover Editorial Team - Health content editors

Reviewer: Calculover Editorial Team - Clinical content reviewer

Last reviewed: 2026-07-23

Last verified: 2026-07-23

Data effective: 2026-07-23

Methodology

Uses the published Jackson & Pollock (1978) men's and Jackson, Pollock & Ward (1980) women's sex-specific regression equations for the 3-site and 7-site skinfold protocols to estimate body density, then converts to body fat percentage via the Siri (1961) equation, classified against standard sex-specific body-fat-percentage category ranges.

Assumption: Skinfold measurements are taken accurately in millimeters at the correct anatomical sites, ideally averaged over 2-3 readings per site.

Assumption: The user is an adult within roughly the study-validated age range (about 18-61 for men, 18-55 for women).

Limitations & guidance

Skinfold-based estimates depend heavily on measurer technique and typically carry a margin of error of roughly ±3-4% compared to reference methods such as DEXA.

The regression equations were derived from specific study populations and may be less accurate for individuals with very low or very high body fat, unusual fat distribution, or ages outside the original validation range.

Professional guidance: This calculator is for educational purposes only and is not medical advice. It cannot replace an assessment by a qualified healthcare professional or a clinical body-composition method. Consult a professional for an individual assessment.

Primary sources

Jackson AS, Pollock ML. Generalized equations for predicting body density of men. British Journal of Nutrition 40(3):497-504 (1978).

Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Medicine and Science in Sports and Exercise 12(3):175-182 (1980).

Siri WE. Body composition from fluid spaces and density: analysis of methods. 1961. Nutrition 9(5):480-491 (reprinted 1993).

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Glossary

Key Terms Explained

7 terms

Skinfold A pinch of skin and the underlying layer of subcutaneous fat, measured in millimeters with a caliper at a specific anatomical site to estimate body fat.

Caliper A spring-loaded pinching tool used to measure skinfold thickness. Consistent technique — pinching firmly, measuring 1cm below the fingers, and taking the reading a few seconds after applying the caliper — matters more than the specific caliper brand.

Jackson-Pollock formula A family of sex-specific regression equations, developed by Jackson and Pollock in 1978 (men) and with Ward in 1980 (women), that estimate body density from the sum of several skinfold measurements and age.

Body density The mass of the body per unit of volume, typically expressed in grams per cubic centimeter. Because fat tissue is less dense than fat-free tissue (muscle, bone, organs), a lower body density corresponds to a higher body fat percentage.

Siri equation The formula %Body Fat = 495/Body Density - 450, published by William Siri in 1961, used to convert a measured or estimated body density into a percentage of body fat.

3-site vs 7-site Two versions of the Jackson-Pollock protocol that trade measurement effort for precision: the 3-site version uses fewer skinfold sites for a faster estimate, while the 7-site version measures more sites and is generally considered slightly more accurate.

Lean mass The portion of total bodyweight that is not fat — muscle, bone, organs, and water. Calculated here as bodyweight minus estimated fat mass.

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Scenarios

Real-World Examples

3 worked examples

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Male, 3-site

Age 25, chest 10mm, abdomen 22mm, thigh 19mm

Sum of skinfolds 51 mm Age 25

Body density = 1.10938 - 0.0008267x51 + 0.0000016x51^2 - 0.0002574x25 ≈ 1.0649. Body fat = 495/1.0649 - 450 ≈ 14.8%, which falls in the "Fitness" range for men (14-18%) — a lean, fit result common among regularly active men.

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Female, 3-site

Age 30, triceps 15mm, suprailiac 12mm, thigh 23mm

Sum of skinfolds 50 mm Age 30

Body density = 1.0994921 - 0.0009929x50 + 0.0000023x50^2 - 0.0001392x30 ≈ 1.0514. Body fat = 495/1.0514 - 450 ≈ 20.8%, which falls in the "Fitness" range for women (14-21%), near the upper edge.

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7-site protocol

Age 35, seven sites summing to 120mm

Sum of skinfolds 120 mm Age 35

Body density = 1.112 - 0.00043499x120 + 0.00000055x120^2 - 0.00028826x35 ≈ 1.0576. Body fat = 495/1.0576 - 450 ≈ 18.0%, which falls just at the edge of the "Average" range for men (18-25%) — illustrating how the 7-site protocol can land close to a category boundary, where technique consistency matters most.

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Deep Dive

Understanding the Skinfold Body Fat Calculator

3 chapters · 4 min read

The skinfold method estimates body fat percentage from a handful of caliper measurements of subcutaneous fat thickness at specific body sites. This calculator uses the widely-cited Jackson-Pollock 3-site and 7-site protocols, converting your measurements into body density and then into an estimated body fat percentage using the Siri equation.

How the Skinfold Body Fat Calculator works

Jackson and Pollock developed sex-specific regression equations — for men in 1978, and with Ward for women in 1980 — that predict whole-body density from the sum of several skinfold measurements plus age. The 3-site protocol uses chest, abdomen, and thigh for men, and triceps, suprailiac, and thigh for women, reflecting where each sex tends to store more subcutaneous fat. The 7-site protocol measures the same seven locations — chest, axilla, triceps, subscapular, abdominal, suprailiac, and thigh — for both sexes and generally produces a slightly more precise estimate because it averages out site-to-site measurement variation. Once body density is calculated, the Siri equation (%fat = 495/density - 450) converts it into a body fat percentage.

Inputs and what they mean

Every skinfold site should be measured in millimeters with a caliper, pinching a fold of skin and fat clearly separated from the underlying muscle, and taking the reading about 1-2 seconds after the calipers are applied. Because technique has a large effect on the result, take 2-3 readings per site and average them, and try to have the same person measure you each time for consistent comparisons. Age matters because skin compressibility and fat distribution shift somewhat with age, which the regression equations account for. Bodyweight is optional — enter it only if you want the Fat & Lean Mass tab to translate your body fat percentage into pounds or kilograms of fat mass and lean mass.

Limits and edge cases

Skinfold measurements depend heavily on measurer skill and caliper technique — different people measuring the same person, or the same person measuring themselves, can produce noticeably different sums, so treat single readings with caution and prefer averaged, repeated measurements. The published equations were validated on adults roughly ages 18-61 (men) and 18-55 (women); accuracy may be reduced outside those ranges, for very lean or very obese individuals, or for people with unusual fat distribution. Skinfold estimates typically carry roughly a ±3-4% margin of error compared to reference methods like DEXA, and should be treated as a screening estimate to track trends over time rather than a precise or diagnostic measurement.

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Questions

Frequently Asked Questions

6 questions

How accurate is the skinfold method?+

Skinfold-based body fat estimates typically carry about a ±3-4% margin of error compared to reference methods like DEXA, and accuracy depends heavily on consistent caliper technique. Averaging 2-3 readings per site and having the same person measure you each time improves reliability.

Should I use the 3-site or 7-site method?+

The 7-site method measures more locations and is generally considered slightly more precise because it averages out site-to-site variation, but it takes longer. The 3-site method is faster and still reasonably accurate for tracking your own trend over time.

Who can take skinfold measurements?+

Skinfold measurements can be self-administered with practice, but a trained professional (personal trainer, exercise physiologist, or clinician experienced with calipers) will generally produce more consistent, reliable readings than a beginner measuring themselves.

Why do men and women use different skinfold sites?+

Men and women tend to store subcutaneous fat in different areas, so the original Jackson-Pollock research used a different 3-site combination for each sex (chest, abdomen, thigh for men; triceps, suprailiac, thigh for women) to maximize prediction accuracy. The 7-site protocol uses the same sites for both sexes but applies different regression coefficients.

What units does this calculator use?+

Skinfold measurements are entered in millimeters (mm), as read directly off a standard caliper. Bodyweight can be entered in pounds or kilograms using the unit toggle, and the fat/lean mass results are reported in whichever unit you selected.

Is this medical advice?+

No. This calculator is a screening estimate for general educational purposes only and does not constitute medical advice. It cannot replace an assessment by a qualified healthcare professional or a clinical body-composition method such as a DEXA scan. Consult a professional before making health decisions based on your result.

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