Body fat percentage calculator

Name: Body fat calculator
Author: Richard Injante

US Navy method estimate from your body circumferences.

Content reviewed by Richard Injante Published by SolucionesAhora.com Updated on 2026-10-08 How we verify

Calculator inputs

Results

Enter your values and press “Calculate” to see the result.

Free, no sign-up! What if you could do this without a calculator? A five-minute game with challenges, lives and points. It clicks even when you cannot be bothered.

In short

What it calculates: US Navy method estimate from your body circumferences.
Formula used: Men:
Example: Man of 75 kg, 178 cm, waist 85 cm and neck 38 cm:

Body fat calculator

BMI cannot tell muscle from fat; this method tries to, using body circumferences that better reflect where adipose tissue accumulates.

All you need is a flexible tape measure.

How it works

The method developed by the US Navy relates logarithms of the circumferences to height. For men it uses waist and neck; for women it adds the hips.

Formula

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

Women:
495 / (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450

Worked example

Man of 75 kg, 178 cm, waist 85 cm and neck 38 cm:

Body fat: 17.9%
Fat mass: 13.4 kg
Lean mass: 61.6 kg

Explanation

The circumference method came from the Navy

The most widespread formula for estimating body fat with a tape measure comes from a United States Navy study in the 1980s. It was designed to screen recruits quickly and cheaply, not to give an exact figure to an individual. That origin explains both its convenience and its limits.

How far off it can be

Against reference methods such as densitometry, circumference formulas can be three or four percentage points out, and more in very lean or very muscular people. They work for tracking a trend; they do not support claiming an exact number.

How to measure so it is useful

Always at the same time, preferably fasted, with the tape snug but not tight, parallel to the floor and not compressing the skin. Consistency matters more than absolute accuracy: if you measure the same way each time, the trend will be reliable even if the value is not.

Bioimpedance scales

They estimate fat by passing a weak current, and the result depends heavily on hydration, time of day and whether you have eaten or trained. They give very different figures for the same person within a single day.

Frequently asked questions

How do I measure correctly?

Waist at navel height, neck just below the Adam’s apple and hips at their widest point. Do not pull the tape tight and breathe normally.

How accurate is it?

The margin is usually ±3 percentage points against a DEXA scan. That is enough to track changes over time.

How accurate are these formulas?

Within three or four points of laboratory methods, and less accurate in very lean or very muscular people. They are useful for tracking a trend.

Are bioimpedance scales reliable?

They depend heavily on hydration and time of day. They measure consistently if you always use them under the same conditions.

Sources and references

The formula behind this calculator is not ours. These are the sources it comes from, in APA 7 format, in case you want to go to the original or cite them in your own work.

Jackson, A. S., & Pollock, M. L. (1978). Generalized equations for predicting body density of men. British Journal of Nutrition, 40(3), 497–504. https://doi.org/10.1079/BJN19780152 The skinfold equations nearly every estimate relies on.
Deurenberg, P., Weststrate, J. A., & Seidell, J. C. (1991). Body mass index as a measure of body fatness: Age- and sex-specific prediction formulas. British Journal of Nutrition, 65(2), 105–114. https://doi.org/10.1079/BJN19910073 The formula that estimates fat percentage from BMI, age and sex.

Need to calculate something else?

These tools are often used alongside this calculator.