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Body Fat Calculator

Estimate your body fat percentage from a few tape measurements with the U.S. Navy method. The body fat calculator also shows your fat mass, lean mass, and fitness category.

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Sex
Units

Body fat
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For general information. Not medical advice.

How to use the Body Fat Calculator

  1. Choose your Sex and your units.
  2. Measure and enter your height, Neck, and Waist at the navel. Women also enter Hip at the widest point. Add your weight if you want fat and lean mass.
  3. Press Calculate. Your body fat percentage appears with its category, and fat and lean mass when a weight is given.

How it works

Men:   % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
fat mass = weight × % ÷ 100
lean mass = weight − fat mass

All lengths are in centimetres. Inches are converted first. ACE categories for men: essential fat 2-5%, athletes 6-13%, fitness 14-17%, average 18-24%, obese 25% and up. For women: 10-13%, 14-20%, 21-24%, 25-31%, and 32% and up.

Examples

  • Male, 180 cm, neck 38 cm, waist 85 cm: log10(47) = 1.6721 and log10(180) = 2.2553, so the result is 16.1%, in the fitness range.
  • The same man at 80 kg carries about 12.9 kg of fat and 67.1 kg of lean mass.

How to measure

  • Use a soft tape, snug but not pressing into the skin, and measure in the morning before eating.
  • Neck: just below the larynx, sloping slightly down at the front.
  • Waist: at the navel for men; at the narrowest point for women. Breathe out normally and do not pull the stomach in.
  • Hip: around the widest part of the buttocks.
  • Take each measurement twice and use the average.

Limitations

  • A waist that is not larger than the neck gives an error, because the logarithm is undefined.
  • A tape estimate is less precise than a lab method such as a DEXA scan or underwater weighing, and the error tends to grow for very lean or very heavy people.
  • Results are for adults and are not a medical diagnosis.

Sources

Frequently asked questions

How accurate is the Navy body fat method?

It is an estimate. The U.S. Navy built the equation by comparing tape measurements of sailors with body fat measured by underwater weighing, so a lab method is more precise for any one person. Measuring carefully, and twice, matters more than anything else you control.

What is a healthy body fat percentage?

The American Council on Exercise lists 18-24% as average for men and 25-31% for women. Athletes are usually lower.

Why does the calculator need my neck size?

The formula uses the neck as a stand-in for lean mass and subtracts it from the waist, which reflects abdominal fat.

Often used together with Body Fat Calculator.

  • BMI Calculator

    Body mass index from height and weight, with the WHO adult category.

  • BMR Calculator

    Calories your body burns at rest, with daily needs by activity level.