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Body Fat Calculator

Estimate body fat percentage from tape measurements, with fat and lean mass.

Method
Sex

Choose a sex, then enter your height, weight, neck and waist to see the result.

For fat around the middle, see the Waist-to-Height Ratio.

Estimates your body fat percentage from a few tape measurements and your height, with the US Navy circumference equations, and splits your weight into fat and lean mass. Without a tape it estimates body fat from your BMI, age and sex instead. Every calculation runs in your browser.

Measuring

Measure with the tape level, and read the waist after a normal breath out. The Department of Defense instruction behind the equations takes each measurement three times, at these sites:

  • Neck — just below the Adam's apple, with the tape at right angles to the neck.
  • Waist, men — around the belly button.
  • Waist, women — at the narrowest point, usually about halfway between the belly button and the bottom of the breastbone.
  • Hip, women — around the widest part of the buttocks, seen from the side.

Each field takes centimetres or inches, and height also feet and inches. The no-tape method needs your age instead.

How it works

Every measurement is converted to inches and one equation runs, as the 2002 DoD instruction prints it, so the same body gives the same result in either unit. The centimetre equations often seen elsewhere are a separate fit, not a conversion, and give a slightly different figure. The result is shown to one decimal; a waist no larger than the neck (for women, waist and hip together), or a result below 2% or above 60%, asks you to check the measurements.

Hodgdon, who developed the equations, puts their standard error at about 3.5 percentage points. The no-tape method is Deurenberg's adult equation, with a standard error of 4.1 points; it was fitted on adults and slightly overestimates body fat in people with obesity. Fat mass is your weight times the percentage, and lean mass the rest.

Under Other estimates of lean mass, the Boer, James and Hume formulas estimate lean body mass from height and weight alone. James's gives a falling lean mass past a certain weight for your height and sex, so it is not shown there.

Men: body fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76 (inches)
Women: body fat % = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (inches)
No tape: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (men 1, women 0)

Examples

A man, 178 cm, 82 kg, neck 38 cm, waist 90 cm

Body fat is 20.3%: a fat mass of 16.6 kg and a lean mass of 65.4 kg.

A woman, 165 cm, 64 kg, neck 33 cm, waist 72 cm, hip 98 cm

Body fat is 27.2%, with 17.4 kg of fat and 46.6 kg lean.

No tape: a woman of 30, 165 cm and 64 kg

With No tape (BMI), a BMI of 23.5 gives 29.7%.

Rules and sources

The tape equations and the measuring sites are from Enclosure 3 of DoD Instruction 1308.3 (2002), which credits the Naval Health Research Center reports by Hodgdon and Beckett (1984). The DoD now screens with the waist-to-height ratio and no longer prints the equations. The no-tape equation is Deurenberg, Weststrate and Seidell (1991). The lean mass formulas are Boer (1984) and James (1976), as Caruso and colleagues (2018) give them, and Hume (1966).

Sources

Reviewed

Frequently asked questions

It is an estimate from a few circumferences, typically within about 3.5 percentage points of a lab measurement, and it depends on measuring each site the same way. A DEXA scan measures fat directly. The tape is most useful for following your own change over time.
The ranges quoted online mostly come from a fitness organisation's table that is no longer on its site and leaves gaps between its bands. For fat around the middle, the waist-to-height ratio has bands from NICE.

See also