STEADFAST • BODY COMPOSITIONEstimate body fat.
Understand the limits.
Use height and waist circumference to estimate body fat percentage with the Relative Fat Mass equation.
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For adults aged 20 and older. Enter your measurements; changing units converts them.
For imperial height, 6 feet = 72 inches; 6 feet 7 inches = 79 inches. Age checks eligibility and is not part of the formula.
How to measure your waist
Stand relaxed. Place a nonstretch tape around your abdomen at the level just above the top of your hip bones. Keep it horizontal and snug without compressing the skin. Measure after breathing out normally, without pulling your stomach in. Use this same location each time, rather than trouser size or the narrowest part of your waist.
The Relative Fat Mass formula
The male equation is 64 − 20 × (height ÷ waist). The female equation is 76 − 20 × (height ÷ waist). Height and waist use the same units. The original study evaluated these equations against DXA in adults aged 20 and older.
What this estimate cannot tell you
The study used male and female sex categories. Its equations are not validated for every hormonal or clinical situation. No body fat rating, diagnosis, or goal weight is assigned here. Do not use waist based estimates during pregnancy or when a hernia, abdominal swelling, or fluid retention distorts the measurement. Consider a qualified assessment when accuracy matters.
Source: Woolcott and Bergman, Relative Fat Mass study, 2018