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Body Fat Calculator

The United States Navy circumference method offers a quick estimate using a tape measure rather than laboratory equipment, and it has been refined against thousands of service members. Enter four measurements and this calculator returns a percentage, your estimated lean mass and the category band your result falls in.

Enter values

Women's equation adds the hip measurement

Converts the percentage into lean mass

Straight below the Adam's apple, tape relaxed

Men: at the navel. Women: at the narrowest point

Widest point — used only for women

Results update as you type.

Results

Body fat (US Navy method)
20.8%
Category
Average
Lean body mass
59.4 kg
Measurement used
Height, neck and waist

How is the Body Fat calculated?

You need a tape measure, not a scanner. For men it compares waist and neck circumference against height; for women it adds the hip measurement, since fat distribution around the hips matters. Circumferences are converted from centimetres to inches because the published constants were fitted on imperial data, then a logarithm of the ratio to height produces the percentage. Your total weight then gives lean mass, and the percentage is placed in a category band that differs by sex.

Formula

Men: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. Women: 160.94 × log10(waist + hip − neck) − 288.53 × log10(height) + 1. Log arguments are in inches (cm ÷ 2.54); lean mass = weight × (1 − body fat ÷ 100).

Example

A man measuring 175 cm tall with a 38 cm neck and a 90 cm waist converts to 68.90 in height, 14.96 in neck and 35.43 in waist. The waist-minus-neck difference is 20.47 in, so body fat = 86.010 × log10(20.47) − 70.041 × log10(68.90) + 36.76 ≈ 112.12 − 124.39 + 36.76 = 20.8%, which sits in the average band for men. At 80 kg that leaves roughly 63.4 kg of lean mass. A woman of 165 cm with a 34 cm neck, 72 cm waist and 98 cm hip comes out near 26.7%.

Things to remember

Circumference estimates are consistent enough to track change over time, but they are not a dexa scan, so treat the number as directional. Measure at the same point of the day with the tape snug rather than tight, and watch the trend across weeks instead of one reading.

Frequently Asked Questions

How accurate is the US Navy body fat method?

It typically lands within two to four percentage points of laboratory testing for most people, which is good enough to follow progress but not to quote as a medical figure. Use it repeatedly under identical conditions and the trend stays reliable.

How do I take the measurements correctly?

Measure the neck at its narrowest point just below the Adam's apple, the waist at the navel, and the hips at the widest point of the buttocks. Take each reading twice, breathe out normally before recording, and repeat at the same time of day so hydration does not skew comparisons.

What body fat percentage is considered healthy?

For men, essential fat sits below about six percent, fourteen to twenty four percent is a typical healthy span and above twenty five is classed as obese. For women the bands are higher: below fourteen is essential, twenty one to thirty one healthy and above thirty two obese.

Does this calculator work if I am very muscular?

Less well, because circumference formulas cannot tell muscle from fat around the midsection. If your training history puts you outside the ordinary range, treat the output as a rough guide and consider a professional body composition test instead.

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