Body Fat Calculator
Measure your neck, waist (and hips for women) with a tape measure to estimate your body fat percentage, fat and lean mass, and where you sit on the ACE chart.
- Free
- No sign-up
- Private
Just below the Adam's apple.
Horizontally at the navel.
- Fat mass
- 29.6 lb
- Lean body mass
- 150.4 lb
- BMI
- 25.8
- BMI-based estimate (Deurenberg)
- 21.7%
| Category | Body fat |
|---|---|
| Essential fat | 2–5% |
| Athletes | 6–13% |
| Fitness | 14–17% |
| Average | 18–24% |
| Obese | 25% and over |
How this was calculated
- Waist − neck = 86.36 − 39.37 = 46.99 cm; log10 = 1.67201.
- log10(height 177.8 cm) = 2.24993.
- Body density term: 1.0324 − 0.19077 × 1.67201 + 0.15456 × 2.24993 = 1.06118.
- Body fat = 495 ÷ that − 450 = 16.5%.
- Fat mass = weight × body fat = 81.6 kg × 16.5% = 13.4 kg; lean mass = 68.2 kg.
The Navy formula is an estimate, typically within 3–4 percentage points of lab methods. For general information, not medical advice.
How this body fat calculator works
This body fat calculator uses the U.S. Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and still used for military fitness standards. It needs only a tape measure. Fat tends to collect around the waist, while the neck mostly reflects frame and muscle, so the gap between them (plus hips for women, who carry more fat there) predicts body density surprisingly well once height is taken into account.
In centimetres, the formula for men is %BF = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women it is 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450. Imperial measurements are converted to centimetres first, so both unit systems give the same answer. As a cross-check, the calculator also shows the Deurenberg estimate, which uses only BMI, age and sex.
Worked example
A man 178 cm (5 ft 10 in) tall with a 50 cm neck and a 96 cm waist: waist − neck = 46 cm, log10(46) = 1.6628 and log10(178) = 2.2504. The denominator is 1.0324 − 0.19077 × 1.6628 + 0.15456 × 2.2504 = 1.0630, and 495 ÷ 1.0630 − 450 = 15.6% body fat, in the "fitness" range. At 70 kg that is about 11 kg of fat and 59 kg of lean mass. A woman 165 cm tall with a 34 cm neck, 76 cm waist and 100 cm hips comes out at about 29.4%, in the "average" range.
How to measure
Use a flexible tape, stand relaxed and measure on bare skin. Neck: just below the larynx, with the tape sloping slightly down toward the front. Waist: men at the navel, women at the narrowest point, at the end of a normal breath out, without sucking in. Hips (women): around the widest part of the buttocks with feet together. Take each measurement two or three times and use the average; a 1 cm error at the waist moves the result by almost a full percentage point.
Common mistakes
- Pulling the tape tight. Compressing the skin lowers the waist reading and the result.
- Measuring the waist at the belt line. For men the formula was built on the navel measurement; jeans usually sit lower.
- Comparing different methods. Smart scales, calipers, DEXA and this formula each have their own bias. Track changes with one method instead of comparing numbers across them.
When the result is misleading
The Navy method is typically within 3–4 percentage points of lab measurements, but it can overestimate body fat in very muscular people with thick necks and underestimate it in people who carry fat on the hips and thighs rather than the belly. It is a population formula for adults, not children or pregnant women. Use it to follow your own trend over weeks, and pair it with the protein calculator and BMR calculator if you are trying to lose fat while keeping muscle.
Frequently asked questions
How does the Navy body fat calculator work?
It uses the U.S. Navy circumference equations (Hodgdon and Beckett, 1984), which estimate body density from height, neck and waist for men, plus hips for women. A man 178 cm tall with a 50 cm neck and 96 cm waist comes out at about 15.6%.
How accurate is the Navy body fat method?
Within about 3 to 4 percentage points of lab methods for most people, similar to a good bioimpedance scale. It is less accurate for very muscular or very lean people, and measuring technique matters more than the formula.
Where do I measure my neck, waist and hips?
Neck just below the larynx, sloping slightly down to the front. Men measure the waist horizontally at the navel; women at the narrowest point. Women measure hips at the widest part of the buttocks. Keep the tape snug but not compressing the skin, and don't suck in.
What is a healthy body fat percentage?
According to the American Council on Exercise, 14–17% is "fitness" and 18–24% "average" for men; 21–24% is fitness and 25–31% average for women. 25% and over for men and 32% and over for women is classed as obese.
Why is my body fat different from the BMI estimate?
The BMI estimate (Deurenberg formula) only knows your weight, height, age and sex, so it cannot tell muscle from fat. The tape measure method uses your waist, which tracks fat more directly; trust it over the BMI estimate if they disagree.