Skinfold Body Fat Calculator

A skinfold test estimates body fat from the thickness of pinched folds of skin and fat at set points on the body. The readings are added up, put into an equation that predicts body density, and the density is turned into a body fat percentage.

What Skinfold Thickness Measures

A caliper measures a double layer of skin plus the fat just under it, in millimeters. It cannot reach fat around your organs, so the equations rely on the link between fat under the skin and total body fat, found by comparing skinfolds with lab-measured body density¹ ² ³.

The Formula

Jackson-Pollock 3-site, men (chest, abdomen, thigh): density = 1.10938 - 0.0008267 x S + 0.0000016 x S² - 0.0002574 x age

Jackson-Pollock 3-site, women (triceps, suprailiac, thigh): density = 1.0994921 - 0.0009929 x S + 0.0000023 x S² - 0.0001392 x age

Jackson-Pollock 7-site, men: density = 1.112 - 0.00043499 x S + 0.00000055 x S² - 0.00028826 x age

Jackson-Pollock 7-site, women: density = 1.097 - 0.00046971 x S + 0.00000056 x S² - 0.00012828 x age

Durnin-Womersley 4-site: density = c - m x log10(S), with c and m set by your sex and age group

Body fat % (Siri) = 495 / density - 450

S is the sum of your skinfolds in millimeters. The equations come from Jackson and Pollock (men, 1978)¹, Jackson, Pollock and Ward (women, 1980)², and Durnin and Womersley (1974)³, and the density step uses Siri's equation⁴.

How This Calculator Computes Your Result

Choose a method, then enter your sex, age and the skinfold sites the method asks for:

Enter the average of your readings for each site, in millimeters. The tool shows your body fat percentage to 1 decimal place, plus your body density, your skinfold total and a second estimate from the Brozek equation (Durnin and Womersley found no significant difference between the two³). Add your weight in kg or lb to see fat mass and lean mass.

What Your Result Means

Your result is placed in an American Council on Exercise (ACE) category⁷. These are fitness guides, not medical cut-offs.

ACE describes 25 to 31% for women and 18 to 24% for men as the average range⁷. If your result is under the essential fat range, recheck your readings, because skinfold equations are least accurate in very lean people³.

How to Measure Correctly

Standard practice is to measure on the right side of the body while standing upright⁵:

• Pinch the fold between thumb and finger, then place the caliper 1 cm from your fingers, square to the fold, halfway between the top and base of the fold. Keep pinching while you read⁵.

• Read the dial 1 to 2 seconds after the jaws close, not longer⁵.

• Take at least two readings per site, moving around the sites in turn, and take another if two differ by more than 1 to 2 mm⁵. Enter the average.

These follow ACSM-style site rules⁵. For the Durnin-Womersley method, take the suprailiac fold just above the hip bone in line with the middle of the armpit, as in the original study³. Mark your sites and use the same ones each time.

How Accurate Are Skinfold Equations?

The published Jackson-Pollock equations have a typical error of about 3.4 points of body fat for men and 3.9 points for women⁶. Durnin and Womersley reported that in two thirds of people the error was within 5 points for men and 3.5 points for women³.

Results can be less accurate in groups unlike the original volunteers. In 1,129 young white, Hispanic and African-American adults, the 3-site equations read lower than a DXA scan (a low-dose X-ray body scan) by 1.3 points in men and 3.0 points in women on average, and the authors judged them inaccurate for this diverse group⁶. Earlier studies using a more detailed four-part lab model found underestimates of about 6 points⁶.

Skinfolds vs the Navy Tape Method

Our Body Fat Calculator uses the US Navy method, which needs only a tape measure: height, neck, waist and (for women) hips. Skinfolds need a caliper and practice, but they measure fat under the skin at several points. The two can give different numbers for the same person, so pick one and stick with it when tracking change.