Body fat calculator
Body fat calculator with a tape measure.
EstimateBody fat (US Navy method)
Estimate from tape measurements. Measure the same way each time and watch the trend.
It estimates your body fat percentage from a few tape measurements with the US Navy method, and adds lean mass and FFMI when you enter your weight.
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How it works
The US Navy method estimates body fat from your height and a few circumferences, all in centimetres. Measure with a soft tape, snug but not pressing into the skin, standing relaxed rather than pulling your stomach in:
Men: body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
FFMI = lean mass in kg ÷ (height in m)²
Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
Neck: just below the larynx (Adam's apple), with the tape sloping slightly down at the front. Waist: horizontally at the navel, after a normal breath out. Hip (women only): around the widest part of the buttocks, with your feet together.
Lean mass is your weight minus fat mass. FFMI (fat-free mass index) is lean mass divided by height squared, and normalized FFMI adjusts it to a height of 1.8 m so people of different heights can be compared.
Example: a man who is 180 cm tall with a 38 cm neck and an 85 cm waist comes out at about 16.1% body fat, in ACE's Fitness category. At 80 kg that is 12.9 kg of fat and 67.1 kg of lean mass, for an FFMI of 20.7 (normalized 20.7).
Body fat categories
Body fat categories from the American Council on Exercise (ACE).
| Men | Women | |
| Below essential fat | under 2% | under 10% |
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% or more | 32% or more |
Common questions
How accurate is the US Navy method?
It is an estimate from body circumferences, so it will not match a DEXA scan or other lab methods exactly, and the result depends a lot on measuring the same way each time. It works best for tracking change: measure under the same conditions every few weeks and watch the trend.
What is a healthy body fat percentage?
The American Council on Exercise groups body fat into essential fat, athletes, fitness, average and obese, with different ranges for men and women, as shown in the table above. Where you should be depends on your health, age and goals, so a doctor can help you judge your own number.
What is FFMI?
Fat-free mass index is your lean mass in kilograms divided by your height in metres squared. It describes how much muscle and other lean tissue you carry for your height. The normalized version, following Kouri and colleagues, adjusts it to a height of 1.8 m so taller and shorter people can be compared.
Why do women also measure their hips?
Women tend to store more fat around the hips, so the US Navy equation for women adds the hip measurement to the waist and subtracts the neck. The men's equation only uses waist minus neck, which is why the hip field only appears when you select female.
How often should I measure?
Every two to four weeks is plenty, because body fat changes slowly. Measure at the same time of day, before eating, with the same tape and technique. Small differences between two measurements are often just measuring error, so look at the trend over a couple of months.
Related calculators
Calorie database: Calories and macros per 100g and per serving for everyday foods.
Sources
Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984 (Reports 84-11, 84-29).
American Council on Exercise (ACE): body fat categories.
Kouri EM et al. Clin J Sport Med 1995;5(4):223-8 (normalized FFMI).
Formula and text last reviewed on 24 September 2026.
This calculator gives general estimates for healthy adults and is not medical advice. If you are pregnant, breastfeeding, or have a medical condition or an eating disorder, talk to a doctor or dietitian before changing how you eat.