ZapKit

Body Fat Calculator

All you need is a measuring tape. Enter your height, neck and waist (and hips, for women) to estimate your body fat percentage and how much of your weight is fat and lean mass.

What is a body fat calculator?

A body fat calculator estimates what share of your body weight is fat. Unlike BMI, which only uses height and weight, body fat percentage reflects body composition, so two people of the same weight can get very different results.

This calculator uses the US Navy circumference method, developed by Hodgdon and Beckett in 1984 and still used by the US military. It needs only your height and a few tape measurements, works in centimetres or inches, and shows your body fat percentage, its category on the American Council on Exercise scale, and your fat and lean mass if you add your weight.

How to use the Body Fat Calculator

  1. 1.Measure

    Neck below the Adam's apple; waist at the navel for men or the narrowest point for women; hips at the widest point.

  2. 2.Enter the numbers

    In centimetres or inches, with your height and, for fat mass, your weight.

  3. 3.Read your result

    Body fat %, its category, and the split between fat and lean mass.

Example: a man and a woman

Measurements in centimetres:

Man: 178 height, 38 neck, 90 waist
about 20.1% body fat
Category
Average (18–24%)
Woman: 163 height, 33 neck, 76 waist, 98 hips
about 29.5% body fat
Category
Average (25–31%)

Men: 495 ÷ (1.0324 − 0.19077 log₁₀(waist − neck) + 0.15456 log₁₀(height)) − 450

Both fall in the average range; for the man, losing about 3 cm from the waist would move him close to the fitness range.

How accurate is the tape method?

The US Navy formula was built from comparisons with underwater weighing, and in studies it usually lands within about 3–4 percentage points of lab methods for most people. It's less reliable at the extremes, for very lean athletes or people with obesity, and small measuring mistakes matter because the formula uses the difference between waist and neck.

Its real strength is tracking change: measure the same way every few weeks and watch the trend rather than one reading.

Frequently asked questions

What's a healthy body fat percentage?

By the American Council on Exercise, about 14–24% is fit to average for men and 21–31% for women. Essential fat alone is 2–5% for men and 10–13% for women.

Why do women measure their hips?

Women store more fat around the hips, so the women's formula adds hip size for a better estimate.

Is this better than BMI?

It estimates fat directly, so it separates muscular people from those carrying extra fat, which BMI can't.

Why does it say my numbers can't be right?

The formula needs your waist to be larger than your neck (or waist plus hips, for women). Check the units and measurements.

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