Estimate body fat percentage with a tape measure
Your weight alone can’t tell you how much of you is fat and how much is muscle, bone and water. This body fat calculator uses the US Navy circumference method to estimate your body fat percentage from your height, neck, waist and (for women) hip measurements.
You also get your fat mass and lean mass in kilograms or pounds, the category you fall into on the American Council on Exercise (ACE) chart, and a second estimate from your BMI and age (the Deurenberg formula) so you can see how the two methods compare.
Two extras sit alongside the Navy method: a US Army mode (abdomen-only legacy tape equation plus the current waist-to-height check) and a lean body mass table using the Boer, James and Hume formulas. Results are estimates for healthy adults rather than medical advice, and they are best used to track change over time.
How to use the Body Fat Calculator
- Choose metric (cm, kg) or imperial (in, lb) and select male or female.
- Enter your age, height and weight.
- Measure your neck just below the larynx (Adam’s apple), with the tape sloping slightly down at the front.
- Measure your waist: men at the navel, women at the narrowest point. Women also measure the hip at its widest point.
- Read your body fat percentage, category, fat mass and lean mass. Measure again in the same way every 2–4 weeks to track progress.
Body Fat Calculator features
US Navy formula, both versions
Uses the published centimetre and inch formulas rather than a rough conversion.
Fat mass and lean mass
Splits your weight into fat and everything else, useful for protein targets.
ACE categories by sex
Shows your band from essential fat to obese, with the full chart below.
Second opinion from BMI
The Deurenberg equation estimates body fat from BMI, age and sex for comparison.
US Army mode
Abdomen, weight and age give the legacy Army percentage, the maximum for your age band and the waist-to-height ratio.
Three lean-mass formulas
Boer, James and Hume side by side, plus lean mass from a body fat figure you already have.
The US Navy body fat formulas
Hodgdon and Beckett developed the method at the Naval Health Research Center in 1984 by comparing tape measurements with underwater weighing.
Men (cm): %BF = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450.
Women (cm): %BF = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450.
Men (inches): %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. Women (inches): %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387.
Example: a man 178 cm tall with a 38 cm neck and 86 cm waist has about 17.2% body fat, in the ACE fitness band. The inch version is a separate regression, so results can differ by a few tenths of a per cent.
ACE body fat categories
Essential fat is the minimum needed for hormones, nerves and organ protection; women need more because of reproductive function. Dropping below it is dangerous.
| 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 |
Deurenberg BMI-based estimate
The 1991 Deurenberg equation is %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex is 1 for men, 0 for women). BMI can’t tell muscle from fat, so it overestimates fat in muscular people. When the two numbers disagree widely, trust the tape measurements more.
US Army mode
The Army used a one-site tape test under Army Directive 2023-11 (June 2023) and AR 600-9: abdomen at the navel, three readings averaged. Men: %BF = −26.97 − 0.12 × weight (lb) + 1.99 × abdomen (in). Women: %BF = −9.15 − 0.015 × weight (lb) + 1.27 × abdomen (in). The maximum is 20/22/24/26% for men and 30/32/34/36% for women at ages 17–20, 21–27, 28–39 and 40+.
Status as of October 2026: the Army announced on 7 July 2026 (Army Directive 2026-13) that it replaced height and weight tables, the tape test and supplemental body fat assessments with a waist-to-height ratio, where under 0.55 meets the standard. This page shows that ratio too. The percentage is the Army’s screening arithmetic, not a medical body-fat measurement; confirm with your unit.
Lean body mass formulas
With weight W in kg and height H in cm, men: Boer = 0.407W + 0.267H − 19.2; James = 1.10W − 128(W/H)²; Hume = 0.3281W + 0.33929H − 29.5336. Women: Boer = 0.252W + 0.473H − 48.3; James = 1.07W − 148(W/H)²; Hume = 0.29569W + 0.41813H − 43.2933. They are population equations that ignore your actual body composition, so they can differ by several kilograms.
Tips for accurate measurements
- Measure in the morning, before eating, on bare skin, with the tape level and snug.
- Take each measurement three times and use the average, with the same tape and spots each time.
Body Fat Calculator FAQ
How accurate is the US Navy body fat calculator?
For most adults it lands within about 3–4 percentage points of laboratory methods such as DEXA. Careful, repeatable measuring matters most.
What is a healthy body fat percentage?
For general health, roughly 14–24% for men and 21–31% for women falls in the fitness and average bands of the ACE chart. Athletes are often lower; going below essential fat (2–5% for men, 10–13% for women) is unsafe.
Why do women need a hip measurement?
Women store more fat on the hips and thighs, so the female formula adds hip to waist.
Is body fat percentage better than BMI?
For an individual, usually yes: it separates fat from muscle, so it isn’t fooled by an athletic build. BMI is still useful as a quick screen — try the BMI calculator alongside this one.
Is the Army body fat calculator still the official standard?
No. The percentage tape test was replaced in July 2026 by a waist-to-height ratio under 0.55, so the Army mode is shown as a legacy reference. Check Army Directive 2026-13 and your unit.
How do I use lean mass?
Lean mass helps set protein targets and is the input for the Katch-McArdle equation in the BMR calculator. If your weight drops but lean mass holds steady, you are losing mostly fat.
How often should I measure my body fat?
Every two to four weeks is plenty; daily readings mostly capture water and measuring error.