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How Body Fat Percentage Is Estimated From Measurements

See how the US Navy tape measure method and the BMI method estimate body fat, how to measure correctly, the standard ranges, and their limits.

By Calculator Tools Team2 min read

  • health
  • fitness
A large 16.1% on a white card over a yellow background, showing an estimated body fat from neck, waist, and height measurements

Body fat percentage is the share of your weight that is fat. A lab scan can measure it directly, but you can also estimate it at home from a tape measure. This article is for information only and is not medical advice.

The tape measure method

The US Navy method estimates body density from your height and the difference between your waist and neck measurements. For women it also uses the hips. It then turns density into a percentage. It does not need your weight or age.

Take a man who is 180 cm tall with a 38 cm neck and an 85 cm waist. The method gives about 16.1% body fat.

The BMI method

The second approach uses a formula that combines BMI, age, and sex. For a 35-year-old man with the same height and a weight of 80 kg (a BMI of 24.7), it gives about 22.3%.

The two answers differ because they look at different things. The tape method looks at body shape, while the BMI method works from weight for height, so it cannot tell muscle from fat.

How to measure

  • Neck: place the tape just below the Adam’s apple, angled slightly down toward the front. Do not flare the neck.
  • Waist: men measure at the navel. Women measure at the narrowest part of the waist.
  • Hips (women): measure around the widest part, keeping the tape level.
  • Use a flexible tape, keep it snug without squeezing, and measure in the morning. Take each measurement twice and average them.

What the numbers mean

The American Council on Exercise ranges are:

Category Women Men
Essential fat 10–13% 2–5%
Athletes 14–20% 6–13%
Fitness 21–24% 14–17%
Average 25–31% 18–24%
Obese 32% and above 25% and above

Women have higher ranges because they need more essential fat. Using these ranges, the man in the first example is in the fitness range.

Limits to keep in mind

Any estimate from measurements can be off by several percentage points, and the BMI method may overstate fat in muscular people. Use the same method each time and look at trends rather than a single number. Methods such as DXA scans, skinfold calipers, and hydrostatic weighing measure more directly.

Fat mass and lean mass

Multiply your weight by your body fat percentage to get your fat mass. The rest is lean mass. At 80 kg and 16.1%, fat mass is about 12.9 kg and lean mass is about 67.1 kg.

Try it yourself

Our body fat percentage calculator supports both methods in metric or imperial units, and it can show how much fat you would lose to reach a goal. It cannot replace advice from a doctor or dietitian.