Body Fat Calculator (US Navy Method)

Enter your height and your tape-measured neck and waist (and hip, for women) to estimate your body fat percentage with the US Navy circumference method; add your weight to see fat mass and fat-free mass too.

Last updated: 28 Oct 2026

Estimated body fat18.7%

Estimated body density1.0561 g/ml
Fat mass15.0 kg
Fat-free mass65.0 kg

How it is calculated

These equations were developed by Hodgdon and Beckett at the US Naval Health Research Center (NHRC) in 1984: the men’s equation from 602 Navy personnel aged 18–56 (report 84-11) and the women’s from 214 personnel aged 18–44 (report 84-29), against body density measured by underwater weighing. The reports give a correlation with underwater weighing of 0.90 for men and 0.85 for women and a standard error of 3.52 percentage points for men and 3.72 for women; cross-validation on other samples found 2.70 for men and 4.04–4.36 for women. So the result is an estimate that can be a few points off, not a measurement. The calculator does not put the result into a category: the “athletic / fit / obese” charts seen online are not part of this method, and we could not verify a primary source for them.

Formula

Men: Density = 1.0324 − 0.19077 × log10(abdomen − neck) + 0.15456 × log10(height)
Women: Density = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)
Fat % = 495 ÷ Density − 450

All lengths are in centimetres (the coefficients were fitted in cm; inches give a wrong result). For men the abdomen is measured at the navel; for women the waist at the narrowest part of the abdomen (about midway between the bottom of the breastbone and the navel) and the hip at the greatest protrusion of the buttocks; the neck just below the larynx. Weight is not in the equation; it is only used for fat mass = weight × fat % ÷ 100 and fat-free mass = weight − fat mass.

Take abdomen − neck (men) or waist + hip − neck (women).
Take the base-10 logarithm of that and of height and apply the coefficients to get body density (g/ml).
Convert density to percent fat with the Siri (1961) equation: 495 ÷ density − 450.
If weight is given, work out fat mass and fat-free mass.

Example

Man, height 178 cm, abdomen 88 cm, neck 38 cm, weight 80 kg: log10(50) = 1.69897 and log10(178) = 2.25042; density = 1.0324 − 0.19077 × 1.69897 + 0.15456 × 2.25042 = 1.05611 g/ml; fat = 495 ÷ 1.05611 − 450 = 18.7%. Fat mass 80 × 0.187 ≈ 15.0 kg, fat-free mass 65.0 kg.

Frequently asked questions

How should I take the measurements?

As in the reports: stand relaxed and use a non-stretch tape that touches the skin without pressing in. The neck goes just below the larynx with the tape sloping slightly down to the front; the abdomen and waist are measured at the end of a normal breath out, at right angles to the body. The reports recorded measurements to the nearest millimetre.

Why are different sites measured for men and women?

Each equation uses the measurements that best predicted body density in its own sample. For men that was the abdomen at the navel and the neck; for women the waist at its narrowest point, the hip and the neck. So the men’s equation should not get the narrowest waist, nor the women’s the navel-level measurement.

How accurate is the result?

In the development studies the standard error against underwater weighing was 3.52 percentage points for men and 3.72 for women, so for about two people in three the true value lies within that much of the estimate. Because the equations were built on adult Navy personnel, they are less reliable for children, in pregnancy and for very different body types.

Why is weight optional?

In both reports weight and age were tried as predictors but did not enter the equation; body fat comes from height and circumferences alone. Weight is only used to turn that percentage into kilograms (fat mass and fat-free mass).

Source

Waist-to-Hip Ratio CalculatorCalculate your waist-to-hip ratio from your waist and hip measurements. Compare the ratio and your waist with WHO cut-offs and learn how to measure.BMI CalculatorCalculate your body mass index from height and weight. See your WHO category and the normal weight range for your height.BMR Calculator (Basal Metabolic Rate)Estimate your basal metabolic rate with the Mifflin–St Jeor, Harris–Benedict or Katch–McArdle equation and compare the equations side by side.Ideal Weight CalculatorCalculate the WHO normal-BMI weight range for your height and the Hamwi, Devine, Robinson and Miller ideal body weight results, with each formula’s origin and limits.