Skinfold Body-Fat Calculator
Use this skinfold body-fat calculator to estimate body-fat percentage with the Jackson–Pollock 3-site or 7-site method.
Choose the site set, enter your age and sex, then record only the selected caliper sites in millimeters. Use the same tester, side and landmarks when you compare results.
See your estimated body-fat percentage, selected skinfold sum and method details. Add bodyweight for estimated fat mass and fat-free mass, meaning the rest of your bodyweight after estimated fat mass, then save a same-method baseline.
Read your skinfold estimate
Your result uses the selected Jackson–Pollock site set, sex and caliper readings. Keep those choices and the millimeter readings with the percentage when you save or compare it.
The 3-site and 7-site methods are separate protocols. A 3-site result does not become a 7-site result by adding extra readings after the calculation.
Calculate above to see your estimate and the readings behind it.
Take the selected caliper readings consistently
Choose 3-site or 7-site, then enter only the sites shown on the form. Use 3-site when you have its sex-specific three readings; use 7-site when you can repeat all seven readings with the same tester and landmarks. Men and women use different 3-site sets; the 7-site set includes all seven named locations for both equations.
- 3-site, men
- Chest between the front armpit line and nipple, abdomen beside the bellybutton and front thigh.
- 3-site, women
- Back of upper arm, front thigh and above the hipbone.
- 7-site, men or women
- Chest between the front armpit line and nipple, side ribcage near the middle of the armpit, back of upper arm, below the shoulder blade, abdomen, above the hipbone and front thigh.
- Reading units
- Record every skinfold in millimeters (mm).
- Repeat readings
- Use the same side, landmarks, fold direction and caliper timing with a trained tester.
See how the selected skinfold sum changes the estimate
Before you calculate, the chart shows an example. After you calculate, it updates to your selected site set, sex, age and readings. Nearby readings show sensitivity to measurement changes; they do not predict your true body-fat range or provide a confidence interval.
| Input or result | Value |
|---|---|
| 35 mm selected-skinfold sum | 10.6007% body fat |
| 40 mm selected-skinfold sum | 12.1202% body fat |
| 45 mm selected-skinfold sum | 13.6149% body fat |
| 50 mm selected-skinfold sum | 15.0844% body fat |
| 55 mm selected-skinfold sum | 16.5280% body fat |
Follow the Jackson–Pollock and Siri calculation
The calculator adds the selected readings and converts that total into an estimated body-fat percentage. The named source equations and conversion details are available below.
The men’s equations come from Jackson and Pollock (1978); the women’s equations come from Jackson, Pollock and Ward (1980). The method accepts men aged 18–61 and women aged 18–55, matching the published equation populations. It does not provide a general health category.
Which site set should I use?
Use the 3-site set when you want the shorter sex-specific protocol and can repeat its exact landmarks. Use the 7-site set when you can collect all seven readings consistently. Keep 3-site and 7-site results as separate baselines.
See the calculation details
| Input or result | Value |
|---|---|
| Selected method | Jackson–Pollock 3-site or 7-site |
| Skinfold units | Millimeters (mm) |
| Density output | Shown to 7 decimal places |
| Body-fat conversion | Siri: 100 × (4.95 ÷ density − 4.50) |
| Optional fat mass | Bodyweight × body-fat percentage ÷ 100 |
| Optional fat-free mass | Bodyweight − estimated fat mass |
Check a complete male 3-site example
This checked example uses a 30-year-old man with a 10 mm chest fold, 20 mm abdomen fold and 15 mm thigh fold. The selected sum is 45 mm.
| Input or result | Value |
|---|---|
| Sex and age | Male, 30 years |
| Selected sites | Chest 10 mm + abdomen 20 mm + thigh 15 mm |
| Skinfold sum | 45 mm |
| Estimated body density | 1.0676965 |
| Estimated body fat | 13.61% |
| Optional bodyweight | 80 kg |
| Estimated fat mass | 10.89 kg |
| Estimated fat-free mass | 69.11 kg |
The numbers are an illustrative calculation from the named equation and are not a target or a claim about measurement accuracy.
Understand the method limits
Jackson–Pollock equations estimate body density from caliper readings. Technique, tester skill, caliper timing, site placement and the source population affect the result. A different site protocol should be kept as a separate method.
The men’s 1978 paper studied 403 men aged 18–61. The women’s 1980 paper studied 249 women aged 18–55. The 7-site method is also described in a later method-use paper. These age limits are part of the method boundary, not health recommendations.
- Jackson and Pollock (1978) — generalized equations for predicting body density of men.
- Jackson, Pollock and Ward (1980) — generalized equations for predicting body density of women.
- Smith-Ryan, Blue, Trexler and Hirsch (2018; online 2016) — later seven-site method-use confirmation.
- Siri conversion: body-fat percentage = 100 × (4.95 ÷ density − 4.50), applied after the named density equation.