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Body Fat Calculator

Measure your height, neck and waist (and hips if you are a woman) and enter your weight. You get your estimated body fat percentage, your fat and lean mass and a category.

Your numbers

Result

Estimate for information only, not professional advice. Last reviewed .

How we calculate it

The US Navy method (Hodgdon and Beckett, 1984) estimates body fat from circumferences, with lengths in inches. For men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.

Fat mass is your weight times the body fat percentage, and lean mass is the rest. The category uses a common scale from the American Council on Exercise: for men, essential fat to about 5%, athletes 6 to 13%, fitness 14 to 17%, average 18 to 24% and obese 25% and over. For women the same bands start at 14%, 21%, 25% and 32%. A man 70 inches tall with a 15 inch neck and a 34 inch waist comes out at about 17.5%.

Assumptions and limits

  • This is an estimate for general information. It is not medical advice and cannot replace a conversation with a doctor or dietitian.
  • Measure the same way each time. Men usually measure the waist at the navel and women at the narrowest point, the neck just below the larynx and the hips at the widest point. A difference of an inch changes the answer a lot.
  • The method can be off by several percentage points, and it is not a medical measurement of body composition. Other scales exist and use different category boundaries.

Frequently asked questions

How does the Navy method work out body fat?

It uses the relationship between your waist, neck, hip and height measurements and body composition measured in a large group of service members. Bigger waists compared with the neck and hips mean more fat.

How accurate is it?

It is a rough estimate. It can be off by several percentage points, and it works best for people with a typical build. Scans or skinfold tests by a professional are more reliable.

What is a healthy body fat percentage?

It depends on age, sex and fitness. The scale shown is one common guide, and a doctor can tell you what is right for you.

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Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: Units = US (pounds, feet and inches); Sex = Male; Height (inches for US units, centimeters for metric) = 70; Neck (inches or centimeters) = 15; Waist (inches or centimeters) = 34; Weight (pounds for US units, kilograms for metric) = 180.

  • Body fat 17.51%
  • Category Fitness
  • Fat mass 31.5 lb
  • Lean mass 148.5 lb

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.