Body Fat Calculator

Two estimates, and the tape measure is the better one. The US Navy circumference formula needs your neck, waist and height, and hips too for women. The other needs nothing but weight, height and age, and pays for it: the Deurenberg formula reads a trained person high and a sedentary light person low. Both formulas are written out below.

Sex

Age

Method

Height

Waist circumference (at navel)

Neck circumference

Weight (optional — for fat/lean mass)

How this is calculated

Two methods, and the one you choose matters more than anything else on the page.

The tape-measure method is the US Navy circumference formula. For men it is 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450, with every measurement in centimetres. For women the hips join the waist: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450. Because the terms are logarithms of differences between measurements, a centimetre of tape error moves the answer by more than a centimetre's worth — measure at the same spot, relaxed, without pulling the tape tight.

The other method needs no tape at all. It works out body mass index as weight in kilograms over height in metres squared, then applies the Deurenberg prediction: 1.20 × BMI + 0.23 × age − 10.8 for men (nothing for women) − 5.4. It is the weaker of the two and the page says so: BMI cannot tell muscle from fat, so a heavily trained person reads high and a sedentary light person reads low.

Both results are clamped to between 2 and 60 percent, because outside that range the formulas are extrapolating rather than estimating. Fat and lean mass are then your weight split by that percentage, which is arithmetic and carries every bit of the original error with it. Neither method is a scan. If the number matters to you medically, get one.

Where this comes from

1. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas — Deurenberg, Weststrate & Seidell, British Journal of Nutrition, 1991 (PubMed)
2. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height (Report No. 84-11) — Hodgdon & Beckett, Naval Health Research Center, 1984

Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy. Method last checked 21 August 2026.

Body fat percentage is a far more meaningful measure of health and fitness than weight alone. Two people at the same weight can look completely different and face very different health risks depending on their body composition.

For those practising intermittent fasting, tracking body fat gives you a clearer picture of whether your fasting protocol is working. Scale weight can fluctuate with water retention, but body fat percentage reveals the true changes happening beneath the surface.

Frequently Asked Questions

How accurate is the US Navy body fat method?

The US Navy method is accurate to within about 3-4% of DEXA scan results for most people. It uses circumference measurements of the neck, waist, and hips to estimate body fat. While not as precise as clinical methods, it is reliable for tracking changes over time.

What is a healthy body fat percentage?

For men, 10-20% is generally considered healthy, with 14-17% being the fitness range. For women, 18-28% is healthy, with 21-24% as the fitness range. Essential fat minimums are about 2-5% for men and 10-13% for women.

Does intermittent fasting reduce body fat specifically?

Research suggests that intermittent fasting can be particularly effective at reducing visceral fat (the dangerous fat around organs) compared to standard calorie restriction alone. IF may also help preserve lean muscle mass during weight loss, improving your overall body composition.

What is the difference between body fat percentage and BMI?

BMI is a simple ratio of weight to height and does not distinguish between muscle and fat. Body fat percentage measures the actual proportion of fat in your body. A muscular person could have a high BMI but a low body fat percentage, making body fat the more useful metric.

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