Body Fat Calculator (US Navy Method)
Body fat percentage describes how much of your weight is fat, which is a more useful picture of body composition than weight or BMI alone — two people with identical BMI can have very different amounts of fat and muscle. The US Navy method estimates it with a tape measure: height, neck and waist for men, with hips added for women. It is not as precise as a DEXA scan or a skinfold test by a trained practitioner, but it needs no equipment beyond a tape, it is repeatable, and it is good at showing change over time. This calculator works in centimetres or in feet and inches.
How to use the body fat calculator (us navy method)
- Choose your units and sex — the formulas were fitted separately for men and women.
- Measure with a flexible tape, relaxed and not pulling it tight: neck below the larynx, waist at the navel (men) or narrowest point (women), and hips at their widest point (women only).
- Enter height and the measurements; for imperial height use feet and extra inches.
- Repeat measurements two or three times and use the average. Track the trend over weeks rather than reacting to a single value.
Formula
Metric form of the US Navy equations (measurements in cm): men: body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450. The result is converted from body density to percent fat using the Siri equation. The method has a typical error of about 3–4 percentage points.
Worked examples
A man, 5 ft 10 in
A man 5 ft 10 in tall with a 15 in neck and 34 in waist: estimated body fat 17.4%, category “Fitness”.
A woman, 165 cm
A woman 165 cm tall with a 33 cm neck, 76 cm waist and 98 cm hips: 28.9% — “Average”.
Why waist changes matter
For the man above, a 2-inch smaller waist (32 in) with everything else the same drops the estimate to 13.4% — waist is the most sensitive input, so measure consistently.
Body-fat categories and how to measure
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% |
| Above average | 32%+ | 25%+ |
Measuring well
- Measure in the morning, before eating, standing relaxed.
- Keep the tape snug but not compressing the skin, parallel to the floor.
- Take each measurement three times and average.
The estimate is best used to watch trends. Pair it with the BMI calculator and calorie calculator.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A woman 5 ft 6 in tall, neck 13 in, waist 30 in, hips 39 in. What is her estimated body fat?
Show answer
Estimated body fat: 28.8% · Category (ACE ranges): Average
Common mistakes to avoid
- Pulling the tape too tight or measuring at different points each time. Consistent technique matters more than the absolute number.
- Using the result as a precise value. The method is an estimate with several percentage points of error.
- Applying it to children, pregnant women or very muscular athletes, for whom the formula is less reliable.
- Mixing units, such as entering inches with metric selected. The calculator warns about implausible values.
- Comparing to BMI categories. Body-fat ranges are different from BMI ranges and differ between men and women.
Frequently asked questions
How accurate is the US Navy body fat method?
It typically agrees with laboratory methods within about 3–4 percentage points for average adults, which is good for tracking change but not for precise measurement.
What is a healthy body fat percentage?
Using the ACE categories, men are typically considered “fitness” at 14–17% and “average” at 18–24%; women at 21–24% and 25–31% respectively. Healthy ranges vary with age and health status.
Where should I measure my waist?
For men, at the level of the navel; for women, at the narrowest point of the waist. Stand relaxed, breathe out normally and keep the tape level.
Why do women need a hip measurement?
Women store fat differently, and the equation fitted for women uses hip circumference along with waist and neck.
How is this different from BMI?
BMI compares weight and height only; body fat percentage estimates composition, so it can separate a muscular person from one with excess fat at the same weight.
Is this medical advice?
No. It is an educational estimate. Discuss any health concerns with a doctor.
Sources and further reading
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.