Donaldson R F Body Fat Calculator
Get a rough estimate of body fat percentage from a few measurements. Everything is calculated in your browser — nothing is stored or sent.
For information only — not medical advice. These formulas give a rough estimate for adults (18+) and can be several percentage points out. They are not suitable for children, pregnant women or people with a medical condition, and they cannot diagnose anything. For health decisions, or if you are worried about your weight or eating, speak to your GP or a registered dietitian.
How the estimates work
The US Navy method uses the difference between waist and neck (plus hips for women) relative to height. Measure with a soft tape, relaxed, and breathe out normally. The BMI-based formula (Deurenberg) estimates from BMI, age and sex; it tends to overestimate in muscular people and underestimate in older adults.
The category names come from the American Council on Exercise ranges, which are general reference points, not targets or diagnoses. Body fat is best tracked over time using the same method; DEXA scans and clinical assessments are far more accurate than any formula.