How to use the body fat calculator
- Choose Metric (cm, kg) or US units (ft, in, lb).
- Pick your sex. The Navy formula is different for men and women, and women also need a hip measurement.
- Enter your age. Only the BMI-based estimate uses it.
- Enter your height and weight.
- Measure your neck just below the Adam's apple, and your waist: at the navel for men, at the narrowest point for women. Women also measure the hips at the widest part of the buttocks.
Keep the tape level and snug without pressing into the skin, and measure after breathing out normally.
How body fat is calculated
The main result uses the circumference equations developed at the Naval Health Research Center by Hodgdon and Beckett. They work in inches, so metric entries are converted first:
The tape measurements stand in for the fat stored around your middle, and height scales them to your frame. The BMI method needs no tape at all. It uses BMI, age and sex, so it can't tell muscle from fat, and it's shown only as a comparison. Fat mass is your weight times the body fat percentage. Lean mass is everything else: muscle, bone, organs and water.
Worked example
These are the calculator's defaults: a 35-year-old man, 175 cm, 70 kg, neck 38 cm, waist 84 cm.
- In inches: height 68.90 in, neck 14.96 in, waist 33.07 in, so waist − neck = 18.11 in
- log10(18.11) = 1.2579 and log10(68.90) = 1.8382
- 86.010 × 1.2579 = 108.19, and 70.041 × 1.8382 = 128.75
- Body fat: 108.19 − 128.75 + 36.76 = 16.2%, in the ACE "Fitness" range for men (14–17%)
- Fat mass: 70 × 0.162 = 11.3 kg, leaving 58.7 kg of lean mass
- BMI method: BMI 22.86, so 1.20 × 22.86 + 0.23 × 35 − 10.8 − 5.4 = 19.3%
The two methods are 3 points apart here. That's a normal gap: the BMI method has no information about your waist.
Body fat categories
| Category (ACE) | 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% or more | 25% or more |
These ranges come from the American Council on Exercise. Women carry more essential fat than men because of breast tissue and fat linked to reproductive hormones, so every band sits higher. Body fat also tends to rise with age even at a steady weight, as muscle is slowly lost.
How accurate is it?
Tape methods are estimates. Against lab methods such as DEXA scans, the Navy formula is usually within about 3 to 4 percentage points for most adults. It can be further off for very muscular people, for people with obesity, and for anyone whose fat is stored mainly on the hips and thighs. Small measuring errors matter: at the default inputs, a waist reading 1 cm too large adds about 0.8 of a percentage point. For tracking change, measure at the same time of day, in the same spots, and watch the trend over weeks. If your result is very low or very high, or you have health concerns, talk to a doctor. They can arrange a more accurate test.
Frequently asked questions
What is a healthy body fat percentage?
The ACE "Fitness" and "Average" bands cover most healthy adults: roughly 14–24% for men and 21–31% for women. Going below the essential fat level (about 2–5% for men and 10–13% for women) is harmful. Your doctor can suggest a target that suits your age and health.
Why do the Navy and BMI results differ?
They use different information. The Navy method measures where you carry fat, while the BMI method only knows your height, weight, age and sex. A muscular person usually gets a lower Navy result than BMI result, and someone with a large waist but normal weight gets a higher one.
Is this the test the U.S. military uses?
Not anymore. These equations were the Navy's tape test for decades, and versions of them were used across the Department of Defense. The services have since moved to simpler screens. The Army now uses a waist-to-height ratio; see the Army body fat calculator for its current standard.
Where exactly should I measure my waist?
Men measure around the navel. Women measure at the narrowest point between the ribs and hips, usually a little above the navel. Keep the tape horizontal, relax your stomach, and take the reading after a normal breath out.
Related calculators
- BMI Calculator — Your body mass index, weight category and healthy weight range, in metric or US units.
- Lean Body Mass Calculator — Lean body mass from your height and weight with the Boer, James and Hume formulas, plus the body fat each implies.
- Army Body Fat Calculator — Check the U.S. Army's current body composition standard: a waist-to-height ratio below 0.55.
- Ideal Weight Calculator — Ideal body weight from the Robinson, Miller, Devine and Hamwi formulas, next to the healthy BMI range.
Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.