Body Fat Calculator

There is no single official cut-off. Gallagher and colleagues (2000) worked out the body fat that corresponds to a BMI of 18.5 to 25 at different ages: 20–39, men 8–19.9% and women 21–32.9%; 40–59, men 11–21.9% and women 23–33.9%; 60–79, men 13–24.9% and women 24–35.9%. The BMI 30 equivalent is 25% to 30% for men and 39% to 42% for women, depending on age. The authors offer these as an approach to guidelines rather than fixed limits, and Asian adults reach each BMI limit at a higher body fat. Enter your age and the calculator compares your result with these ranges.

The US Navy method uses height plus neck and waist circumference for men, and neck, waist and hip circumference for women, in a logarithmic equation. A man who is 178 cm tall with a 38 cm neck and an 88 cm waist comes out at 18.8%; a woman of 165 cm with a 32 cm neck, 72 cm waist and 98 cm hips at 27.7%.

Following the US Navy measurement guide: neck just below the larynx (Adam's apple), with the tape perpendicular to the neck and sloping slightly down at the front. Men's waist: level with the navel, arms relaxed at the sides. Women's waist: at the narrowest point of the abdomen, usually about halfway between the navel and the lower end of the breastbone; if it is hard to find, measure a few spots and use the smallest. Hips: over the greatest protrusion of the buttocks seen from the side, with the tape level. Measure at the end of a normal breath out, keep the tape snug without pressing into the skin, and average three readings.

The equations were fitted to Navy personnel whose body fat was measured by underwater weighing. Their standard error of estimate is 3.52 percentage points for men and 3.61 for women, so your true figure can easily sit a few points either side of the result. Tape technique adds to that: in the examples above, 1 cm more waist moves the result by 0.7 points for the man and 0.5 for the woman. In a newer Navy sample checked against a four-compartment reference, the equations read 0.8 points high for men and 2.0 for women on average. They were developed on service members aged 18–56 (men) and 18–44 (women), so errors can be larger for very lean, very heavy or older people.

The Navy equations estimate body fat from height and circumferences only. If you add your weight, the calculator also shows how many kilograms (or pounds) of that are fat and how much is lean mass: muscle, bone, organs and water.

The men's equation takes the logarithm of waist minus neck, which is undefined when the difference is zero or negative. That usually means a measurement was taken in the wrong place or in the wrong unit, so the calculator says so instead of showing a number.

They answer different questions. BMI uses only height and weight and cannot tell fat from muscle; circumferences capture where fat collects, so they separate a muscular person from an overweight one better. Both are screening estimates, not a substitute for methods such as DEXA.

The Naval Health Research Center recommended these equations to the US Department of Defense in 1999, and the services used them for years. In June 2023 the US Army moved to a one-site tape test under Army Directive 2023-11. This calculator uses the neck, waist and hip method, which is the one most people mean by the Navy method.