Body Fat Calculator
The U.S. Navy method estimates body fat from height, neck and waist (plus hips for women): a man 178 cm tall with an 86 cm waist and a 38 cm neck comes out at about 17.2%, in the fitness range on the ACE chart. Add your weight to see fat mass and lean mass.
By the Calculators With Steps team · Updated November 10, 2026 · How we check our math
- Fat mass
- 13.4 kg
- Lean mass
- 64.6 kgmuscle, bone, organs and water
- ACE category
- Fitnessmen's ranges
- BMI-based estimate (Deurenberg)
- 20.2%from BMI 24.6 and age 30; less precise for muscular people
Step-by-step working
- Waist − neck = 86 − 38 = 48 cm
- log10(48) = 1.68124; log10(height 178 cm) = 2.25042
- Body density = 1.0324 − 0.19077 × 1.68124 + 0.15456 × 2.25042 = 1.05949
- Body fat = 495 ÷ 1.05949 − 450 = 17.2%
- Deurenberg: 1.20 × BMI 24.62 + 0.23 × 30 − 10.8 × 1 − 5.4 = 20.24%
Body fat categories for men (American Council on Exercise)
| Category | Body fat | You |
|---|---|---|
| Essential fat | 2–5% | |
| Athletes | 6–13% | |
| Fitness | 14–17% | ← you |
| Average | 18–24% | |
| Obese | 25% and above |
The Navy tape method agrees with underwater weighing to within about 3.5 percentage points for most people. Measure three times and use the average, and track the trend rather than a single reading. Not designed for children or pregnant women.
How to measure for the body fat calculator
You need a flexible tape measure and a mirror or a helper. Measure on bare skin, standing relaxed, and don’t pull the tape tight or hold your breath.
- Height: without shoes.
- Neck: just below the larynx (Adam’s apple), with the tape sloping slightly downward toward the front.
- Waist, men: around the abdomen at the level of the navel, after a normal breath out.
- Waist, women: at the narrowest point between the ribs and hips.
- Hips, women only: around the widest part of the buttocks.
Take each measurement three times and use the average. Measure at the same time of day each time you check, ideally in the morning.
U.S. Navy body fat formula
The Navy method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984. It predicts body density from circumferences and height, then converts density to body fat with the Siri equation. With all measurements in centimetres:
Men: density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)
Women: density = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)
Body fat % = 495 ÷ density − 450
The Department of Defense also prints an inch-based version (for men, 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76). It gives almost the same answer: for a man 70 in tall with a 15 in neck and 34 in waist, it returns 17.5%, against 17.4% from the centimetre formula this calculator uses.
Worked example
| Man | Woman | |
|---|---|---|
| Height | 178 cm | 165 cm |
| Neck / waist / hip | 38 / 86 cm | 33 / 74 / 98 cm |
| Body density | 1.05949 | 1.03571 |
| Body fat | 17.2% | 27.9% |
| Weight | 78 kg | 62 kg |
| Fat mass / lean mass | 13.4 kg / 64.6 kg | 17.3 kg / 44.7 kg |
| ACE category | Fitness | Average |
For the man: waist − neck = 48 cm, log10(48) = 1.68124 and log10(178) = 2.25042, so density = 1.0324 − 0.19077 × 1.68124 + 0.15456 × 2.25042 = 1.05949, and body fat = 495 ÷ 1.05949 − 450 = 17.2%.
Body fat percentage chart
The American Council on Exercise (ACE) categories are the most widely used:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
Women naturally carry more essential fat, linked to hormones and reproduction, so their ranges sit about 7 to 8 points higher.
How accurate is the tape method?
Against underwater weighing, the Navy equations had a standard error of about 3.5 percentage points for men and 3.7 for women in the original studies. That is similar to skinfold calipers and home bioelectrical impedance scales. DEXA scans and hydrostatic weighing are more precise but cost money and need a clinic or lab.
Errors come mainly from measuring in slightly different places, and the formula can misjudge people with unusual shapes, such as a very thick neck from strength training. The U.S. Army replaced its multi-site tape test with a one-site test in 2023, but the neck-and-waist method remains the best-known tape formula.
Body fat from BMI
If you only know your height, weight and age, the Deurenberg (1991) formula gives a rough estimate:
Body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women)
The man in our example has a BMI of 24.6, which gives 20.2%, about 3 points above his tape result. The woman’s BMI of 22.8 at age 35 gives 30.0%. Because BMI cannot separate muscle from fat, this method overestimates fat in muscular people. You can check your BMI with the BMI calculator.
Using your result
- Track the trend over weeks. A drop in waist size with steady weight usually means you are losing fat and keeping muscle.
- Your lean mass feeds into the Katch-McArdle equation in the TDEE calculator and BMR calculator, which can give a better calorie estimate for muscular people.
- For a target weight range, see the ideal weight calculator.
Body Fat Calculator: frequently asked questions
How do I calculate my body fat percentage at home?
Use a soft tape to measure your neck and waist (and hips if you are a woman), then enter them with your height. The U.S. Navy formula turns them into a body fat estimate. A man who is 178 cm tall with a 38 cm neck and 86 cm waist comes out at about 17.2% body fat.
How accurate is the Navy body fat method?
In the original Navy studies the formula's standard error against underwater weighing was about 3.5 percentage points for men and 3.7 for women. So a reading of 20% usually means somewhere between roughly 16% and 24%. Careful, repeated measurements make it more useful for tracking change.
What is a healthy body fat percentage?
On the American Council on Exercise chart, 14–17% is the fitness range for men and 21–24% for women, and 18–24% (men) or 25–31% (women) is average. Obesity starts at 25% for men and 32% for women. Essential fat, the minimum for normal body function, is about 2–5% in men and 10–13% in women.
Can I calculate body fat percentage from BMI?
Yes, roughly. The Deurenberg formula is: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. For a 30-year-old man with a BMI of 24.6 it gives 20.2%, while his tape measurements give 17.2%. The BMI method can't tell muscle from fat, so the tape method is usually closer.
Why do women measure their hips?
Women store more fat around the hips and thighs, so the women's Navy equation uses waist plus hip minus neck. A woman who is 165 cm tall with a 33 cm neck, 74 cm waist and 98 cm hips comes out at about 27.9% body fat, in the average range.
Is the Army body fat calculator the same as the Navy one?
For decades all U.S. services used the same neck-and-waist (plus hip for women) tape equations. In 2023 the Army moved to a one-site tape test under Army Directive 2023-11, so its current numbers come from a different formula. This calculator uses the classic Navy method.
What is the difference between body fat percentage and BMI?
BMI only compares weight with height, so a muscular person can score as overweight. Body fat percentage estimates how much of your weight is fat, which is closer to what matters for health. Using both, plus your waist size, gives a fuller picture.
How we checked this page: every figure in the examples and FAQs above is produced by this calculator and verified by automated tests against known answers, and the rules and rates come from the sources below. Last updated . Spotted a problem? Tell us.
Sources and further reading