Skin Fold Calculator

What the pinch measures

A caliper cannot see inside you. It pinches a double fold of skin plus the subcutaneous fat sitting directly underneath, at sites researchers picked because they track total body fatness across a lot of people. This tool runs the Jackson and Pollock three-site equations: chest, abdomen and thigh for men, tricep, suprailiac and thigh for women. Your three readings in millimetres are summed, pushed through an age-adjusted equation that estimates body density, and that density is converted into a percentage with the Siri equation. Age is in the formula because fat distribution shifts inward over the years.

How to take a fold properly

Technique error dominates this method more than any other body composition tool here. A practised tester with a cheap caliper will beat a perfect equation and an unsteady hand every single time.

• Pinch and lift about a centimetre away from where the jaws close.
• Let the jaws do the squeezing, and read at roughly two seconds.
• Take each site twice, and use the median if they disagree.
• Same side of the body, same landmarks, same order, every time.
• Measure before training, not after, and keep the same tester.

A worked example

Say you are a 30 year old man reading 12 mm at the chest, 20 at the abdomen and 15 on the thigh. The sum is 47 mm. Run that sum and your age through the male equation and body density lands around 1.0663, which the Siri conversion turns into roughly 14.2 percent body fat, in the Fitness band. Now suppose your pinches ran 5 mm light across the three sites combined. The sum falls to 42 and the estimate drops to about 12.7 percent, a whole category over an error your fingers would never notice.

How it compares to the alternatives

DEXA is the practical reference here, and well-taken skinfolds usually sit within a few percentage points of it. Circumference methods like the Navy tape are easier to self-administer and roughly comparable on average, but a tape cannot tell where fat actually sits. Consumer bioimpedance scales are the most convenient and the least stable, since hydration alone moves a reading between morning and evening. On repeatability, which is what you actually care about, a consistent caliper tester is hard to beat.

Why the trend beats the number

Every method here carries error bars, but a lot of that error repeats itself in the same direction each time you measure. That makes the change between readings far more trustworthy than any one reading on its own. Re-check every three to four weeks, same tester, same conditions, and judge the direction rather than the decimal. If you want a second angle on the same question, compare against the tape-based body fat estimate or turn your percentage into lean body mass, which is often the more useful number to watch. If a reading concerns you, that is a conversation for a doctor, not a calculator.