How it works
BMI can’t tell fat from muscle — a lean bodybuilder can score as “overweight”. Body fat percentage measures how much of your weight is fat, so it is a far better gauge of progress when cutting or building muscle. This calculator uses the U.S. Navy circumference method, which needs only a tape measure and is used for military body-composition standards; it typically lands within about 3–4 percentage points of lab methods.
men: BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450 women: BF% = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.221 × log₁₀(height)) − 450Worked examples. A man 178 cm (5′10″) with a 38 cm neck and 86 cm waist is 17.2% body fat — the “fitness” band. At 80 kg (176 lb) that is 13.8 kg of fat and 66.2 kg lean body mass. A woman 165 cm tall with a 33 cm neck, 75 cm waist and 100 cm hips is 29.4% — “average”.
How to measure
- Neck: just below the larynx (Adam’s apple), tape sloping slightly down at the front.
- Waist, men: horizontally at the navel, at the end of a normal breath out; don’t suck in.
- Waist, women: at the narrowest point, usually above the navel.
- Hips, women: around the widest part of the buttocks.
- Measure in the morning before eating, twice, and use the average. Inches × 2.54 = cm.
Body fat chart (American Council on Exercise)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Women naturally carry more essential fat for hormonal and reproductive health, so compare against the right column. Dropping below essential levels is unsafe.
Lowering body fat without losing muscle
- A moderate deficit of 300–500 kcal a day — set it with the calorie deficit calculator.
- High protein, 1.6–2.2 g/kg — see the protein calculator.
- Resistance training 2–4 times a week and enough sleep.
- Re-measure every 2–4 weeks rather than relying on the scale alone.
Compare with your BMI, or see a healthy weight for your height with the ideal weight calculator.