How to measure
All you need is a flexible tape measure. Measure on bare skin, keep the tape snug but not compressing the skin, and take each reading two or three times, using the average.
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly downward toward the front.
- Waist: for men, horizontally at the level of the navel; for women, at the narrowest point of the abdomen. Relax and don't pull your stomach in.
- Hips (women): at the widest point of the buttocks.
- Height: standing straight without shoes.
Choose your units, enter the measurements and the result appears immediately. Adding your weight lets the calculator split your body into fat mass and lean mass.
The U.S. Navy formula
This method was developed by the U.S. Naval Health Research Center and estimates body density from circumference measurements, then converts density to a fat percentage. In centimeters:
Women: 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.221·log₁₀(height)) − 450
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% |
| Obese | 32%+ | 25%+ |
These bands are widely used by the American Council on Exercise (ACE).
How accurate is it?
Tape-measure methods typically land within 3–4 percentage points of laboratory methods such as DEXA scans. Accuracy depends heavily on consistent measuring technique. For tracking progress, measure at the same time of day under the same conditions; the trend matters more than any single reading.
Worked example
A man who is 178 cm tall with a 38 cm neck and an 86 cm waist has a waist-minus-neck value of 48 cm. Plugging these numbers into the Navy formula gives about 17% body fat, which falls into the "fitness" band. If he weighs 80 kg, that is roughly 13.8 kg of fat mass and 66 kg of lean mass – bones, muscle, organs and water. Repeating the measurement every four weeks shows whether a diet or training plan is reducing fat while preserving muscle, something the scale alone cannot tell you.
Remember that body fat is only one marker of health. Blood pressure, blood sugar, cholesterol, fitness and sleep matter as well, so use this result as one input alongside regular check-ups.
Frequently asked questions
Is the Navy body fat method accurate?
It is usually within a few percentage points of lab methods for most people, which makes it a useful, free way to track changes over time.
Why do women need a hip measurement?
Women typically store more fat around the hips and thighs, so the formula for women includes hip circumference for a better estimate.
What is a healthy body fat percentage?
Roughly 21–31% for women and 14–24% for men is considered fit to average. Very low levels can be unhealthy too.
Is body fat better than BMI?
Body fat percentage tells you about composition, which BMI cannot. Using both gives a more complete picture.
Last reviewed 2026-10-27. This body fat calculator is provided for general information; verify important decisions with a qualified professional.