Skinfold calipers measure the thickness of a pinched fold of skin and the fat just under it. Because about half of the body’s fat lies directly beneath the skin, the thickness of folds at several sites predicts total body fat fairly well. In the 1970s Andrew Jackson and Michael Pollock fitted equations that turn the sum of three or seven skinfolds into body density, and the Siri equation turns density into a percentage of fat. This calculator applies those published equations to your readings.
The method is accurate only if the readings are. Practice on the same sites, use the same caliper and compare results over time rather than treating a single number as exact.
How to use the skinfold body fat calculator
- Choose sex, age and method. The 3-site method uses different sites for men and women; the 7-site method uses the same seven for both.
- Enter your body weight to get fat and lean mass.
- Enter the skinfold readings in millimetres. Only the sites for your chosen method are used: men’s 3-site needs chest, abdomen and thigh; women’s 3-site needs triceps, suprailiac and thigh; 7-site needs all seven.
- Read the body fat percentage, density and category.
Skinfold formulas
Women, 3-site: D = 1.0994921 − 0.0009929 S + 0.0000023 S² − 0.0001392 age
Men, 7-site: D = 1.112 − 0.00043499 S + 0.00000055 S² − 0.00028826 age
Women, 7-site: D = 1.097 − 0.00046971 S + 0.00000056 S² − 0.00012828 age
Body fat % = 495 ÷ D − 450 (Siri)
S is the sum of the skinfolds in millimetres and D is body density in g/cm³. The men’s equations are from Jackson AS, Pollock ML, Br J Nutr 1978;40:497–504; the women’s are from Jackson AS, Pollock ML, Ward A, Med Sci Sports Exerc 1980;12:175–182. The conversion of density to fat is from Siri WE, in Techniques for Measuring Body Composition (National Academy of Sciences, 1961).
Worked example
A 30-year-old man weighing 75 kg with chest 12 mm, abdomen 20 mm and thigh 18 mm.
- Sum S = 12 + 20 + 18 = 50 mm
- Density D = 1.10938 − 0.0008267 × 50 + 0.0000016 × 2,500 − 0.0002574 × 30 = 1.0643
- Body fat = 495 ÷ 1.0643 − 450 = 15.1% (fitness category)
- Fat mass = 75 × 15.1% = 11.3 kg; lean mass = 63.7 kg
Body fat from the 3-site sum
Computed from the formulas above for men (chest + abdomen + thigh) and women (triceps + suprailiac + thigh).
| 3-site sum | Men, age 25 | Men, 40 | Men, 55 | Women, 25 | Women, 40 | Women, 55 |
|---|---|---|---|---|---|---|
| 30 mm | 8.5% | 10.2% | 11.8% | 13.4% | 14.3% | 15.2% |
| 45 mm | 13.1% | 14.7% | 16.4% | 18.8% | 19.7% | 20.6% |
| 60 mm | 17.4% | 19.1% | 20.8% | 23.8% | 24.8% | 25.7% |
| 75 mm | 21.5% | 23.2% | 24.9% | 28.5% | 29.5% | 30.4% |
| 90 mm | 25.3% | 27.0% | 28.8% | 32.8% | 33.8% | 34.8% |
| 105 mm | 28.8% | 30.6% | 32.4% | 36.7% | 37.7% | 38.7% |
Body fat categories
| Category (ACE) | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
The category ranges are from the American Council on Exercise and are descriptive guides for adults.
Measuring tips
- Use the right side of the body, with dry skin, and mark each site.
- Pinch firmly between thumb and finger, pulling skin and fat away from the muscle. Place the caliper jaws 1 cm from your fingers and read after about two seconds.
- Take two or three readings at each site, rotating around the sites, and average them; they should agree within 1–2 mm.
- Measure before exercise, because blood flow and fluid shifts thicken the folds afterwards.
- Use the same caliper and tester for follow-up checks.
Limits
The equations were derived in adults aged roughly 18 to 60 and do not apply to children or older adults without caution. Accuracy drops in very lean or very obese people because pinching is harder. For other estimates try the Body Fat Calculator, YMCA Body Fat Calculator or Navy Body Fat Calculator, and see the Lean Body Mass Calculator and FFMI Calculator for muscle-related measures.
This page is for information only and is not medical or dietary advice. Speak to a doctor or registered dietitian about your own situation.
Sources
- Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr 1978;40:497–504.
- Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc 1980;12:175–182.
- Siri WE. Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition. National Academy of Sciences, 1961:223–244.
- American Council on Exercise. What Are the Guidelines for Percentage of Body Fat Loss? (body fat categories).
Frequently asked questions
How accurate is the skinfold method?
In the hands of a trained tester, the Jackson-Pollock equations predict body fat within about 3 to 4 percentage points of underwater weighing for average adults. Errors are larger for beginners, very lean or very obese people, and when different testers or calipers are used.
Where are the skinfold sites?
Chest: diagonal fold halfway between the nipple and the front of the armpit (men). Abdomen: vertical fold 2 cm beside the navel. Thigh: vertical fold midway between hip and knee on the front. Triceps: vertical fold at the back of the arm, midway between shoulder and elbow. Suprailiac: diagonal fold just above the hip bone. Midaxillary: vertical fold on the side at nipple level. Subscapular: diagonal fold just below the shoulder blade.
Should I take readings on one side?
Yes. Standard practice is the right side of the body. Take each site two or three times in rotation and use the average. Pinch firmly with the thumb and finger, apply the caliper 1 cm away and read after about 2 seconds.
Which method should I use, 3-site or 7-site?
The 7-site equation uses more data points and can be slightly more reliable, but the 3-site version is quicker and works nearly as well. Use whichever you can measure consistently and stay with it to track change.
Why does body density come into it?
The equations estimate how dense your body is. Fat is less dense than lean tissue, so a lower density means more fat. The Siri equation converts density to a body fat percentage by assuming the density of fat and lean tissue are constant.