Body Fat Calculator
- Updated
- Imperial and metric
- Free, no sign-up
Results
Estimated body fat 27.3% by the US Navy method (average, ACE) and 30.6% by the BMI method.
| Category | Body fat | Your results |
|---|---|---|
| Essential fat | 10–13% | |
| Athletes | 14–20% | |
| Fitness | 21–24% | |
| Average | 25–31% | Navy estimate and BMI estimate |
| Obesity range | 32% or more |
Both methods are estimates. In the original studies the Navy equation for men had a standard error of about 2.7 percentage points against underwater weighing, and the BMI formula about 4.1. Measure on bare skin, keep the tape level and snug without pressing in, and repeat each measurement.
This is an estimate from a published formula, not medical advice. Talk to a doctor or registered dietitian about your own situation.
How to use the body fat calculator
- Choose female or male and enter your age, height and weight.
- Measure your neck and waist with a flexible tape, on bare skin and after breathing out normally. Women also measure the hips at the widest point.
- Read the Navy estimate, the BMI-based estimate and the ACE category table. Measure twice: a half-inch error at the waist can move the result by up to about a point.
Body fat formulas
US Navy, women (inches): %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
US Navy, metric (cm): density = 1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height) (men)
density = 1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height) (women); %BF = 495 ÷ density − 450
Deurenberg (BMI): %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women)
James Hodgdon and Marcie Beckett of the Naval Health Research Center derived the circumference equations in 1984 by comparing tape measurements with underwater weighing. The metric version predicts body density, which Siri's equation turns into a fat percentage; the inch version is the form US military body-composition rules used for years, until the services moved to waist-to-height ratio in 2026. The two are separate fits, so they differ slightly: this calculator uses whichever matches the units you choose. The Deurenberg formula (1991) estimates body fat from BMI, age and sex, from a study of 1,229 people aged 7 to 83; this calculator uses the adult version.
Worked example
A 35-year-old woman is 5 ft 5 in (65 in), weighs 140 lb and measures a 13 in neck, 29 in waist and 38 in hips. The Navy equation gives 163.205 × log₁₀(54) − 97.684 × log₁₀(65) − 78.387 = 27.3% body fat (the metric form gives 27% for the same body). That is about 38 lb of fat and 102 lb of lean mass, in the ACE "average" range. Her BMI is 23.3, so the Deurenberg formula gives 1.20 × 23.3 + 0.23 × 35 − 5.4 = 30.6%. A man 5 ft 10 in tall with a 15.5 in neck and a 35 in waist comes out at 18.5%, also in the average range for men.
ACE body-fat categories
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obesity range | 32% or more | 25% or more |
Women carry more essential fat than men, so every band sits higher. ACE labels the top band "obese"; the calculator calls it the obesity range. These bands are a guide for active adults, not a diagnosis: body fat naturally rises a little with age.
Navy estimates for men 5 ft 10 in tall
Generated with the calculator's engine. For a given waist, a thicker neck lowers the estimate because the formula uses the difference between them.
| Waist | Neck 14 in | Neck 15 in | Neck 16 in | Neck 17 in |
|---|---|---|---|---|
| 30 in | 11.1% | 8.7% | 6.1% | 3.3% |
| 32 in | 15.5% | 13.4% | 11.1% | 8.7% |
| 34 in | 19.4% | 17.5% | 15.5% | 13.4% |
| 36 in | 23% | 21.3% | 19.4% | 17.5% |
| 38 in | 26.2% | 24.6% | 23% | 21.3% |
| 40 in | 29.2% | 27.8% | 26.2% | 24.6% |
| 42 in | 32% | 30.6% | 29.2% | 27.8% |
Tips for a reliable reading
- Measure at the same time of day. Morning, before eating, gives the most repeatable waist measurement.
- Keep the tape level. Use a mirror, or ask someone to help. The neck tape slopes slightly down at the front, just below the Adam's apple.
- Track the trend. A single estimate can be a few points off, but the same method used monthly shows the direction of change well.
- Compare methods with care. Smart scales, skinfold calipers and DXA scans all use different assumptions, so their numbers won't match exactly.
For lean mass from height and weight alone, try the lean body mass calculator; for the current Army standard, the Army body fat calculator. This is not medical advice; talk to a doctor or registered dietitian.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center reports 84-11 and 84-29, 1984.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr 1991;65(2):105–114.
- American Council on Exercise, body-fat percentage norms for men and women.
Frequently asked questions
How does the US Navy body fat method work?
It estimates body fat from height and a few tape measurements: neck and waist for men, plus hips for women. The equations, published by Hodgdon and Beckett in 1984, were fitted against underwater weighing. A woman 5 ft 5 in tall with a 13 in neck, 29 in waist and 38 in hips comes out at about 27.3% body fat.
What is a healthy body fat percentage?
There is no single number, but the American Council on Exercise puts average adults at 25 to 31% for women and 18 to 24% for men, with fitness ranges of 21 to 24% and 14 to 17%. Essential fat, the minimum the body needs, is about 10 to 13% for women and 2 to 5% for men.
How accurate is a body fat calculator?
Tape and BMI formulas are estimates. In the original studies the Navy equation for men had a standard error of about 2.7 percentage points and the Deurenberg BMI formula about 4.1, so a reading of 20% could reasonably be anywhere from about 17% to 23%. Lab methods such as DXA are more precise.
Why do the Navy and BMI methods give different answers?
The BMI method only knows your height, weight, age and sex, so it assumes typical muscle mass. The Navy method uses your waist, which tracks body fat more directly. For a muscular person the BMI method usually reads higher; for someone with little muscle it can read lower.
How do I work out fat mass and lean mass?
Multiply your weight by your body fat percentage to get fat mass, and subtract that from your weight for lean mass. At 180 lb and 18.5% body fat, fat mass is about 33 lb and lean mass about 147 lb.