Body Fat Calculator (Navy Method)
Quick answer: The US Navy method estimates body fat from three tape measurements — neck, waist, and (for women) hips — plus height. It tracks within ~3-4% of lab methods for most people and is the best zero-equipment option. Measure at the navel, tape snug but not compressing.
Why body fat beats scale weight
Two people at identical weight and height can look and perform completely differently — composition is the difference. Body fat percentage separates the fat you're trying to lose from the muscle you're trying to keep, which makes it the right metric for judging a cut, a bulk, or a GLP-1 run where muscle preservation is the quiet battle.
Tracking during weight loss
Re-measure every 2-4 weeks under identical conditions. If weight is dropping but waist isn't moving proportionally, the loss may be leaning on muscle — the fix is usually more protein (see the protein calculator) and resistance training, not a bigger deficit.
FAQ
How accurate is the Navy method?+
Studies put it within 3-4 percentage points of DEXA scans for most physiques — accurate enough for tracking change, which is what matters. It drifts most for very lean or very muscular bodies. Whatever its absolute error, measuring the same way each time makes the trend reliable.
When should I measure?+
Morning, before eating, after using the bathroom — waist measurements swing several centimeters through the day with food and water. Consistency of conditions matters more than which conditions.
What's a healthy body fat percentage?+
Broad healthy ranges: men 10-20%, women 18-28%, with athletes below and average populations above. Essential fat floors (~3% men, ~12% women) are survival minimums, not goals.
Educational tool — estimates only, not medical advice. Consult a licensed healthcare provider for individual guidance.