Skinfold Body Fat Calculator (3-Site)

Three caliper pinches, your age and sex. The calculator converts the sum to body density and then to a body-fat percentage.

How the Skinfold, 3-site method works

Sum the three readings (S). Body density: men BD = 1.10938 − 0.0008267·S + 0.0000016·S² − 0.0002574·age; women BD = 1.099421 − 0.0009929·S + 0.0000023·S² − 0.0001392·age. Then Siri: body fat % = 495 ÷ BD − 450.

Worked example

A 25-year-old man with chest 10 mm, abdomen 20 mm and thigh 15 mm (sum 45): BD ≈ 1.0690, so body fat ≈ 13% — the top of the athletic range.

Body-fat ranges (adults)

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Above average	25%+	32%+

Other ways to estimate body fat

U.S. Navy method — tape measure only, the quickest.
Skinfold, 7-site — Seven caliper pinches — the most precise field method.
RFM — Relative Fat Mass — one ratio of height to waist, no caliper.
From BMI — Roughest estimate — from BMI, age and sex, nothing to measure but weight and height.

Whichever you pick, stick with it: the direction over weeks matters more than the exact figure. To lower body fat, run a modest deficit with the calorie calculator, keep protein high via the macro calculator, and lift.

Source: Jackson & Pollock 1978 (men), Jackson, Pollock & Ward 1980 (women). Siri body-density conversion: Siri 1961.

Related calculators

Related guides

Frequently asked questions

Which three sites does the 3-site method use?

For men: chest, abdomen and thigh. For women: triceps, suprailiac and thigh. The equation is sex-specific, so the sites are not interchangeable between the two.

How accurate is the 3-site skinfold method?

Done carefully with a quality caliper, it is typically within about 3 percentage points of a DEXA scan for people in the normal range — better than tape methods, not as good as the 7-site version or a scan. Technique is the main source of error.

Where exactly do I pinch?

Chest: a diagonal fold half-way between the nipple and the front of the armpit (men). Abdomen: a vertical fold about 2 cm to the side of the navel. Thigh: a vertical fold on the front of the thigh, midway between the hip crease and the top of the kneecap. Triceps: a vertical fold on the back of the upper arm, half-way between shoulder and elbow. Suprailiac: a slightly diagonal fold just above the hip bone at the front. Pinch the skin and fat only, not the muscle underneath.

Caliper or tape — which should I use?

If you have a caliper and can measure consistently, skinfolds track fat change more closely than the tape (Navy) method, especially for lean and athletic people. If you only have a tape, the Navy method is fine — just be consistent.

Why does the number jump around between attempts?

Skinfold thickness changes with hydration, and pinch location and pressure vary between attempts. Measure at the same time of day, in the same order, and average two or three readings per site. Trust the trend over a month, not one session.

Last reviewed: September 2026. Figures and formulas are checked against their published sources; see the site's data notes.