Yasin Şükrü Tan

Calculators

Body fat calculator

Two methods: circumference measurements with a tape, or skinfold thickness with calipers. The tape method needs nothing but a tape measure.

Units
Method
Sex

These equations carry different coefficients by biological sex because that is how their reference groups were built. The choice here is not about identity — it selects which set of coefficients to use.

lb
in
in

Just below the larynx, tape sloping slightly down at the front.

in

At navel level, after breathing out.

Result

Fill in the fields and the result appears here.

How to measure

A measurement taken from the wrong place gives the wrong answer. The equations were derived against these specific sites.

  1. 1. Measure in the morning, before eating and after using the bathroom. Circumferences can shift by a couple of centimetres across a day with food and fluid.
  2. 2. Keep the tape in contact with the skin but do not pull it tight. Compressing tissue shrinks the reading.
  3. 3. Keep the tape parallel to the floor; check the back of it in a mirror.
  4. 4. Do not hold your breath. Take the waist reading after a normal exhale.
  5. 5. Measure each site twice; if the two readings differ by more than 1 cm, take a third and use the middle value.
  6. 6. For tracking, always measure under the same conditions: same time of day, same order, same tape.

How it is calculated

The circumference method (commonly called the US Navy equation) estimates body fat from height, neck and waist — plus hip for women. It is widely used because it needs no equipment: everyone has a tape measure.

The skinfold method takes caliper readings from three sites, computes body density first, and converts that to a fat percentage with the Siri equation. Done well it is more accurate than the tape method, but it is very sensitive to the skill of whoever takes the reading — two testers can get noticeably different results on the same person.

Both methods carry a reported error of roughly ±3-4%, and both degrade at the extremes: very lean or very heavy people fall outside the range the equations were derived in. The gold-standard methods (DEXA, hydrostatic weighing, air displacement) are laboratory work.

The real use is not the single number — it is measuring again over time WITH THE SAME METHOD under the same conditions and watching the direction. Even if the absolute value is several points off, the direction of change comes out right, and that is what you plan against.

This is an estimate, not a measurement. The equation is built on a population average; your own value can fall outside that range.

Sources

  • Hodgdon J.A., Beckett M.B. (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Rapor 84-11 / 84-29.
  • Jackson A.S., Pollock M.L. (1978). Generalized equations for predicting body density of men. Br J Nutr 40(3): 497-504.
  • Jackson A.S., Pollock M.L., Ward A. (1980). Generalized equations for predicting body density of women. Med Sci Sports Exerc 12(3): 175-181.
  • Siri W.E. (1961). Body composition from fluid spaces and density: analysis of methods. Techniques for Measuring Body Composition, s. 223-244.

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