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Skinfold Body Fat Calculator

Estimate your body fat percentage from caliper skinfold readings, using the Jackson–Pollock 3-site or 7-site equations and the Siri conversion.

Level: Grades 8–9

Printable worksheet

Skinfold Body Fat Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Sex

The published equations have separate versions for males and females.

Method

Whole years. The equations were developed on adults.

Diagonal fold halfway between the armpit crease and the nipple (men); one third of the way for women.

Vertical fold about 2 cm (an inch) to the side of the navel.

Vertical fold on the front of the thigh, halfway between hip crease and kneecap.

Add it to split your weight into fat mass and lean mass.

Result

Estimated body fat

15.6%

From a 50 mm sum of skinfolds, the Jackson–Pollock 3-site equation gives a body density of 1.063 g/cm³, which the Siri equation turns into about 15.6% body fat. This is an estimate, not a clinical measurement.

Body density
1.063 g/cm³
Sum of skinfolds
50 mm

See the step-by-step solution ↓

Readings used
Readings used
SiteSkinfold (mm)
Chest12
Abdomen22
Thigh16

Step-by-step solution

  1. Add up your 3 skinfolds (chest, abdomen, thigh). The equations use this total, S

    12+22+16=50 mm

  2. Put the total and your age into the 3-site equation for men. It gives your body density: density = 1.10938 − 0.0008267 × S + 0.0000016 × S² − 0.0002574 × age

    1.10938−0.0008267×50+0.0000016×502−0.0002574×35=1.063036 g/cm³

  3. Turn density into body fat with the Siri rule: percent body fat = 495 ÷ density − 450

    4951.063036−450=15.647447%

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

Please note: This calculator gives a general screening estimate, not a diagnosis. Talk to a qualified healthcare professional about your individual health.

What this calculator does

Get an estimate of your body fat percentage from a few skinfold readings. Skinfold calipers are a pinching tool. They measure the thickness of a pinched fold of skin and the fat just under it. A fairly steady share of body fat sits under the skin. So adding up several folds can predict your body density (how heavy you are for your size). Density, in turn, predicts body fat. The Jackson–Pollock equations do this. They were published for men in 1978 and for women in 1980. They are the most widely used method and appear in many exercise-science textbooks.

Choose the 3-site or 7-site version, then enter your sex, your age and your readings in millimeters. The calculator gives your body density. It also gives an estimated body fat percentage, using the Siri equation. If you add your weight, it splits that weight into fat mass and lean mass. This is an estimate for fitness tracking. It isn't a medical measurement or a diagnosis.

Where it's used

Why this math matters outside the classroom:

  • Personal training. Trainers add a client's chest, abdomen and thigh folds of 12, 22 and 16 mm to get the 50 mm sum the equation needs.
  • Exercise science labs. University students compare caliper estimates with underwater weighing to see how prediction equations are built.
  • Sports teams. Team staff record the sum of skinfolds across a season to follow changes in body composition alongside performance.
  • Evaluating a quadratic. Students substitute S = 50 into an expression with an S² term and see how the squared part adds 0.004 to the total.
  • Fat and lean mass. Applying a 15% estimate to a weight of 180 lb splits it into 27 lb of fat mass and 153 lb of lean mass.

How to use it

  1. Select your sex and the 3-site or 7-site method. You'll only see the sites that method uses.
  2. Take each skinfold on the right side of the body, two or three times. Enter the average for each site in millimeters.
  3. Enter your age in whole years, because the equations adjust for age.
  4. Optionally enter your body weight to see fat mass and lean mass.

What the inputs mean

Sex
The published equations have separate versions for males and females.
Method
The 3-site version uses chest, abdomen and thigh for men. For women, it uses triceps (back of the upper arm), suprailiac (just above the hip bone) and thigh. The 7-site version uses chest, midaxillary (side of the chest), triceps, subscapular (below the shoulder blade), abdomen, suprailiac and thigh for both sexes. With more sites, an error at any one site matters less.
Age
The equations were developed on adults, roughly 18 to 60. Each extra year of age lowers the predicted density slightly.
Chest skinfold
Hold the fold firmly between your thumb and finger, about 1 cm above the caliper jaws. Read the dial about two seconds after the jaws close.
Midaxillary skinfold
Vertical fold on the side of the chest, level with the bottom of the breastbone.
Triceps skinfold
Vertical fold on the back of the upper arm, halfway between shoulder and elbow.
Subscapular skinfold
Diagonal fold just below the lower tip of the shoulder blade.
Abdomen skinfold
Vertical fold about 2 cm (an inch) to the side of the navel.
Suprailiac skinfold
Diagonal fold just above the front of the hip bone.
Thigh skinfold
Vertical fold on the front of the thigh, halfway between hip crease and kneecap.
Body weight (optional)
Optional. Weight doesn't change the body fat percentage. It only turns that percentage into fat mass and lean mass.

Formula and method

S = sum of skinfolds (mm)
Men, 3-site:   BD = 1.10938 − 0.0008267 × S + 0.0000016 × S² − 0.0002574 × age
Women, 3-site: BD = 1.0994921 − 0.0009929 × S + 0.0000023 × S² − 0.0001392 × age
Men, 7-site:   BD = 1.112 − 0.00043499 × S + 0.00000055 × S² − 0.00028826 × age
Women, 7-site: BD = 1.097 − 0.00046971 × S + 0.00000056 × S² − 0.00012828 × age
Siri: body fat % = 495 ÷ BD − 450

S is the sum of your skinfolds in millimeters, and age is in years. BD is body density in grams per cubic centimeter (g/cm³). Jackson and Pollock built these equations from people whose density was measured by underwater weighing. The S² term (S times S) lets the line curve. That's because each extra millimeter of skinfold matters slightly less as the sum grows. The age term reflects that, with age, more fat is stored inside the body rather than under the skin.

The Siri equation (1961) turns density into percent fat. It treats the body as two parts. Fat has a density of about 0.9 g/cm³, and everything else is about 1.1 g/cm³. So densities near 1.1 mean very little fat. The calculator rejects readings that would give zero or negative body fat.

Worked example

A 35-year-old man measures chest 12 mm, abdomen 22 mm and thigh 16 mm with calipers, using the 3-site method.

  1. Sum of skinfolds S = 12 + 22 + 16 = 50 mm.
  2. BD = 1.10938 − 0.0008267 × 50 + 0.0000016 × 50² − 0.0002574 × 35 = 1.10938 − 0.041335 + 0.004 − 0.009009 = 1.063036 g/cm³.
  3. Body fat = 495 ÷ 1.063036 − 450 = 15.6%.

Result: His estimated body fat is 15.6%, from a body density of 1.0630 g/cm³.

Understanding the result

Body fat from skinfolds is an estimate. Compared with lab methods, it's typically off by a few percentage points. The skill of the person using the calipers matters as much as the equation.

The most useful reading is often the trend. Have the same person measure the same sites the same way every few weeks. You can then see whether the sum of skinfolds is going up or down, even before turning it into a percentage.

No single number is a health verdict. What's right for you depends on you, and a doctor or other qualified professional can advise on that.

Assumptions and limitations

  • Readings are in millimeters, taken at the standard sites on the right side of the body.
  • The person is an adult, similar to the groups the equations were developed on.
  • Fat and fat-free tissue (everything that isn't fat) have the fixed densities the Siri equation assumes.
  • Accuracy drops for people who are very lean, very muscular, older or high in body fat. It also drops for groups unlike the people in the original studies.
  • How the folds are measured causes much of the error. Readings taken by different people, or with different calipers, can't be compared directly.
  • Not valid for children or during pregnancy.
  • The Siri two-part (two-compartment) model can misjudge body fat in people whose bone or muscle density differs from the average.

Frequently asked questions

Should I use the 3-site or 7-site method?

Both come from the same research, and they give similar results for most people. The 7-site version spreads the measurement over more of the body, so one awkward site matters less. The 3-site version is quicker, and easier to repeat the same way each time.

Where exactly are the skinfold sites?

Chest is a diagonal fold between the armpit and nipple. Abdomen is an up-and-down (vertical) fold beside the navel. Thigh is a vertical fold on the front of the thigh. Triceps is on the back of the upper arm. Suprailiac is just above the front of the hip bone, and subscapular is below the shoulder blade. Midaxillary is on the side of the chest. The hints under each field give more detail.

Why does age change the result?

With age, more fat tends to be stored around the organs rather than under the skin. So the same skinfolds point to a lower body density in an older person. The age term in the equation corrects for that.

How does this compare with the tape-measure method?

Calipers measure fat under the skin directly. The tape (Navy) method works it out from measurements around your body. In skilled hands, calipers are usually a little more precise. But both are rough, outside-the-lab estimates that can be off by several percentage points.

Are my readings stored or shared?

No. The calculation runs in your browser, and this calculator doesn't create a shareable link with your measurements in it.

Sources

How this calculator is checked

Method: Jackson & Pollock (1978) men's and Jackson, Pollock & Ward (1980) women's generalized body density equations (3-site and 7-site quadratic forms with age); Siri (1961) equation for percent fat from body density. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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