Body Fat Calculator (US Navy Method)
Enter your weight, height and a few tape measurements and this body fat calculator shows your body fat percentage, a category, and your fat mass and lean mass, updating as you type. It uses the US Navy circumference method, works in kg and cm or lb and inches, and runs in your browser, so nothing you enter is uploaded.
How this body fat calculator works
There is no Calculate button. Fill in the form and the Body fat figure changes with every keystroke:
- Units: pick Metric (kg, cm) or Imperial (lb, in).
- Biological sex: choose Male or Female. The formula differs, and Female adds a Hip box.
- Weight and Height: decimals are fine.
- Neck, Waist and, for Female, Hip: the tape measurements, explained below.
Until every box holds a usable number the result area asks for your measurements. Body fat shows to one decimal place. If your waist (plus hip, for women) is not larger than your neck, the page warns you to check the numbers.
Body fat = 16.1% (Fitness), fat mass about 12.1 kg, lean mass about 62.9 kg
Woman, 62 kg, 165 cm, neck 32 cm, waist 75 cm, hip 98 cm
Body fat = 28.9% (Average), fat mass about 17.9 kg, lean mass about 44.1 kg
How to measure neck, waist and hip for the Navy method
Use a soft tape, stand relaxed, and keep the tape level and snug without pressing into the skin.
- Neck: just below the larynx (Adam's apple).
- Waist: around the navel for men; at the narrowest point for women.
- Hip: around the widest point of the hips and buttocks (women only).
The result is sensitive to small errors, especially at the waist, so measure twice and use the same spots each time. A tape measure body fat calculator is best for tracking your own trend, not for a single exact number.
The US Navy body fat formula
The calculator uses the Hodgdon-Beckett equations from the US Navy method. With height, neck, waist and hip in centimetres, the page converts inches for you and applies:
Women: 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
The result is kept between 1% and 75%. Weight is not part of the percentage; it is only used to work out fat mass (weight × body fat %) and lean mass (the rest).
Body fat percentage categories for men and women
The label under your result follows the American Council on Exercise ranges:
| Category | Men | Women |
|---|---|---|
| Essential fat | under 6% | under 14% |
| Athletes | 6 to 13.9% | 14 to 20.9% |
| Fitness | 14 to 17.9% | 21 to 24.9% |
| Average | 18 to 24.9% | 25 to 31.9% |
| Obese | 25% and above | 32% and above |
How accurate is the Navy body fat calculator?
Treat it as an estimate from a formula, not a medical measurement. It can differ from a DEXA scan or calipers by several percentage points, and it does not see muscle mass directly. It is a general reference, not medical advice; for health decisions talk to a professional.
Frequently asked questions
How do I calculate body fat with a tape measure?
Measure your neck, waist and (for women) hip with a soft tape, and note your height and weight. The US Navy formula turns those circumferences and your height into a body fat percentage. Enter the numbers in the form on this page and the percentage, fat mass and lean mass update as you type.
Where do I measure my neck, waist and hip for the Navy body fat calculator?
Neck: just below the larynx (Adam's apple), with the tape level. Waist: around the navel for men, and at the narrowest point for women. Hip: around the widest point of the hips and buttocks. Keep the tape snug but not squeezing, stand relaxed and breathe out normally before reading it.
Is the Navy body fat calculator accurate?
It is an estimate, not a measurement. The Navy method is a convenient way to track change over time, but it can be a few percentage points off a DEXA scan or other lab method, and it reacts to small tape errors. Measure the same way, at the same time of day, and compare against your own earlier results.
What is a healthy body fat percentage for women and for men?
This page labels results with the American Council on Exercise ranges. For women: essential fat under 14%, athletes 14 to 20.9%, fitness 21 to 24.9%, average 25 to 31.9%, and 32% and above is labelled obese. For men: under 6%, 6 to 13.9%, 14 to 17.9%, 18 to 24.9%, and 25% and above. The labels describe a range, not a diagnosis.
Why is there no age input in this body fat calculator?
The US Navy circumference formula uses only height, neck, waist and, for women, hip. Age and weight do not change the percentage. Weight is used afterwards to split your body into fat mass and lean mass.
How do I find my lean body mass from my body fat percentage?
Multiply your weight by your body fat percentage to get fat mass, then subtract it from your weight. At 75 kg and 16.1% body fat, fat mass is about 12.1 kg and lean mass about 62.9 kg. This page shows both in kg or lb.
Can I use pounds and inches?
Yes. Switch Units to Imperial and enter weight in lb and height, neck, waist and hip in inches. The formula converts everything to centimetres first, so the result is the same as the metric one.
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