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Calculation of body fat percentage
US Navy method: three simple measurements with a tape measure are enough. More reliable than BMI to determine your body composition.
Why measure your body fat?
Unlike weight or BMI, fat mass percentage distinguishes muscle mass from fat. Two people can weigh the same weight but have radically different compositions: at 70 kg, one can be at 15% body fat (athletic), the other at 28% (sedentary). Monitoring this rate is more relevant than a simple weighing to assess your progress.
The US Navy method
Developed for the American army, this method requires only a tape measure and gives an estimate of ±3% of the DEXA measurement (absolute reference). More accessible than impedancemetry or skin folds, it has been validated by several clinical studies.
Fat mass benchmarks — Men
- 2–5%: essential (competitor in extreme shape)
- 6–13%: athlete
- 14–17%: sporty
- 18–24%: acceptable
- ≥ 25%: excess
Fat mass benchmarks — Women
- 10–13%: essential
- 14–20%: athlete
- 21–24%: sporty
- 25–31%: acceptable
- ≥ 32%: excess
Limits of the estimate
The US Navy formulas slightly underestimate body fat in very muscular athletes and overestimate it in very thin people. For precise monitoring, multifrequency impedancemetry or DEXA remain the reference. As an evolutionary benchmark (before/after a training period), the US Navy method remains very reliable.
Questions fréquentes
Une fois par mois suffit. La graisse corporelle évolue lentement (300-500 g par semaine de déficit calorique). Une mesure plus rapprochée risque de capter du bruit (rétention d'eau, repas).
It is a proxy for lean upper body mass. The US Navy formula subtracts this value to isolate abdominal fat.
For women: 21–31%. For men: 14–24%. Going below the “essential” thresholds (10% women, 5% men) creates hormonal and immune risks.
DEXA (two-photon absorptiometry) with ±1% error. Failing that, multifrequency impedancemetry (±2%), then the US Navy method (±3%). Consumer impedance scales are unreliable (±5–7%).