Brozek Body Fat Percentage Calculator

How it is calculated

The Brozek equation converts body density into body fat: BF% = 457 / D − 414.2, where D is body density in g/cm³. It is the same relationship as the textbook form (4.57 / D − 4.142) × 100. Fat mass is W × BF% / 100 and lean mass is W − fat mass, with W the body weight in kilograms. Both inputs are required. The density must be above 0.9 and at most 1.2, and the tool returns nothing when the computed fat is under 0% or over 75%, which in practice means densities from about 0.935 up to about 1.103. At the same density it gives a slightly lower percentage than the Siri equation.

Common mistakes

• Entering density in kg/m³ (1060) instead of g/cm³ (1.06). The tool rejects values above 1.2, so you get no result.
• Using the percentage form of the formula and the engine form together. The constants 457 and 414.2 already include the factor of 100, so do not multiply the output again.
• Mixing results from Brozek and Siri when tracking progress. They differ by a few tenths of a percentage point at the same density, so stick with one equation over time.
• Typing a very high density such as 1.12. Body fat would be negative, so the tool returns nothing rather than a number.
• Leaving weight blank and expecting at least the percentage. Weight is required, and without it the tool shows no result at all.