Body Fat Calculator

Body fat % = 495 / D − 450

S

Sum of the three skinfold readings, in millimetres (mm)

A

Age in years

D

Body density, in grams per millilitre

Calipers are the cheapest way to track body fat over months: the same tester, the same calipers and the same sites are what make the trend readable. Use a tape measure instead when you have no calipers and want a rough number, and a DEXA scan when you need the number itself rather than its direction. The Jackson and Pollock equations were fitted on adults, so they are not the tool for children or for pregnancy.

1. A 30-year-old man, 80 kg, skinfolds 15 / 25 / 20 mm

   1. Add the three sites: 15 + 25 + 20 = 60 mm
   2. Men's equation: D = 1.10938 − 0.0008267 × 60 + 0.0000016 × 60² − 0.0002574 × 30 = 1.0578
   3. Siri: 495 ÷ 1.0578 − 450 = 17.9%
   4. Fat mass: 80 kg × 17.9% = 14.4 kg; lean mass: 80 − 14.4 = 65.6 kg

   17.9% is inside the range most fitness charts call acceptable for a man in his thirties. Calipers carry a few points of error between testers, so read the figure as a trend rather than as a diagnosis.

2. A 30-year-old woman, 65 kg, skinfolds 20 / 25 / 25 mm

   1. Add the three sites: 20 + 25 + 25 = 70 mm
   2. Women's equation: D = 1.0994921 − 0.0009929 × 70 + 0.0000023 × 70² − 0.0001392 × 30 = 1.0371
   3. Siri: 495 ÷ 1.0371 − 450 = 27.3%
   4. Fat mass: 65 kg × 27.3% = 17.7 kg; lean mass: 65 − 17.7 = 47.3 kg

   A sum of 60 mm reads 17.9% for a man and 24.1% for a woman of the same age, which is why the two equations have separate coefficients. Never compare your percentage against someone of the other sex.

Calipers need practice. Two testers measuring the same person can differ by several points, and pinching too little or too much skin is the usual reason. The equations were derived from adults (men aged 18 to 61, women 18 to 55) and they are age- and sex-specific, so they do not apply to children, to pregnancy, or to bodybuilders at the extremes. At very high readings the curve flattens and understates body fat, and the three sites are assumed to stand in for the whole body. Treat the figure as an estimate for tracking, not as a clinical measurement.

How accurate are skinfold calipers?

For a trained tester measuring the same person repeatedly, calipers are usually quoted as within three to four percentage points of a laboratory method. Between two different testers the gap can be wider, and where exactly you pinch is the largest single source of error. Use one tester, one set of calipers and one set of sites, and the change over months is far more trustworthy than the absolute figure.

Which three sites do I measure?

Men measure the chest (a diagonal fold halfway between the nipple and the front of the armpit), the abdomen (a vertical fold about two centimetres to the right of the navel) and the thigh (a vertical fold midway between the hip crease and the top of the knee). Women measure the triceps (a vertical fold halfway between the shoulder and the elbow, on the back of the arm), the suprailiac (a diagonal fold just above the hip bone) and the same thigh site.

Which side of the body should I measure, and how many times?

Measure the right side of the body, standing, with the muscle relaxed and the arm hanging. Pinch the skin and the fat beneath it, keeping the muscle out of the fold. Take each site twice and, if the two readings differ by more than a millimetre or two, take a third and use the middle value. This calculator takes one reading per site, so average them yourself first.

Can I use this instead of a DEXA scan?

No. DEXA and other laboratory methods measure the number itself and can separate fat from lean tissue region by region. Calipers estimate it from three places and assume the rest of the body follows. What calipers are good at is the direction and size of a change over weeks and months, which is what most people are actually tracking.

Why is this different from what my smart scale says?

Bathroom scales use bioelectrical impedance, which passes a small current through the body and infers fat from how well it conducts. That reading swings with hydration, recent exercise and the time of day, and it is calibrated against a population rather than against you. Calipers and impedance disagree by several points routinely; neither is the reference method.

What is a healthy body fat percentage?

There is no single published band, and the charts you see quoted come from different bodies with different purposes: some are athletic performance standards, some are population risk categories. This page deliberately prints no band for that reason, and because the caliper figure carries a few points of error of its own. For a health screening question, use BMI or a waist measurement instead.

• Nutrition and Athletic Performance — joint position statement — Academy of Nutrition and Dietetics, Dietitians of Canada and American College of Sports Medicine, 2016
• Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults — National Heart, Lung, and Blood Institute, 1998