THE US NAVY METHOD
This calculator uses the US Navy circumference method, developed by Hodgdon and Beckett (1984). It estimates body fat from height, waist, neck, and (for women) hip measurements. Validation studies show it correlates within 3-4% of DEXA scans for most populations. It is the most widely-tested field method that does not require callipers or lab equipment.
WHERE IT IS LESS ACCURATE
The Navy method can underestimate body fat in lean, muscular athletes and overestimate it at very high body fat levels. It relies on circumference ratios, so individuals with unusual fat distribution patterns (visceral vs subcutaneous) may see larger errors. It does not distinguish between different types of lean tissue.
WHEN TO GET A DEXA SCAN
If body composition is central to your performance strategy, invest in a DEXA scan. It is the gold standard for body composition analysis — it gives you precise lean mass, fat mass, and bone mineral density, segmented by body region. One scan establishes your baseline. A second scan 8-12 weeks later measures real change. Most sports performance clinics offer DEXA for $50-150 per scan.
BODY COMPOSITION AND CYCLING PERFORMANCE
Cycling is a gravity sport on climbs and a drag sport on flat terrain. On gradients above 5%, body mass is the dominant variable — which is why the power-to-weight ratio (W/kg) matters more than raw watts for any rider who sees hills. But chasing low body fat without protecting lean mass is a net negative: you lose the muscle that produces power.
Dr. Asker Jeukendrup's work on body composition in endurance athletes emphasises that performance-driven composition changes should be periodised, moderate, and supported by adequate energy intake. The goal is losing fat mass while protecting (or building) lean mass — and the only way to do that is through structured nutrition and training, not restriction.
A NOTE ON ESTIMATION
This tool gives you a directional estimate, not a clinical measurement. Use it for tracking trends over time (measure consistently, same time of day, same conditions) rather than treating any single reading as absolute truth. For precision, get a DEXA scan.