Body Density Calculator

About this calculator

Body density — mass divided by volume, expressed in g/cm³ or g/mL — is estimated from the sum of skinfold thickness measurements taken at several standardized body sites (commonly using the Jackson-Pollock 3-site or 7-site equations), combined with age and sex, since these regression equations were built from population data correlating skinfold thickness with lab-measured density from hydrostatic (underwater) weighing. Once body density is known, the Siri equation (Body fat % = (495 / density) − 450), developed by physicist William Siri in 1961, converts it into an estimated body fat percentage.

Exercise physiologists, athletic trainers, and body-composition labs use skinfold-based body density and the Siri equation as a practical, low-cost alternative to gold-standard methods like DEXA scans or hydrostatic weighing, since a set of skinfold calipers is far cheaper and more portable than either — though accuracy depends heavily on measurement technique consistency, which is why trained testers typically take each skinfold site three times and average the results.

This calculator takes your summed skinfold measurements, age, and sex, computes your estimated body density using the relevant regression equation, and converts it to body fat percentage via the Siri equation.