Body Fat % Calculator
Estimate your body fat percentage using the accurate US Navy circumference method.
How the US Navy Method Works
This calculator uses the US Navy circumference method, developed at the Naval Health Research Center. It estimates body fat percentage from tape measurements of your neck, waist and (for women) hips, combined with height. The formulas are logarithmic:
- Men: 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
All measurements in centimetres. The method works because waist size tracks fat storage closely while neck size tracks lean frame size — the difference between them is a surprisingly good fat signal.
How To Measure Correctly
- Neck: just below the larynx (Adam's apple), tape sloping slightly downward at the front. Don't flare the tape over the trapezius.
- Waist: men measure at the navel; women at the narrowest point. Measure at the end of a normal exhale — don't suck in.
- Hips (women): at the widest point of the buttocks, feet together.
- Use a flexible, non-stretch tape, snug but not compressing the skin, and take each measurement twice.
Body Fat Percentage Categories
| 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 carry more essential fat than men because of reproductive physiology — comparing your number against the men's column (or vice versa) is meaningless.
Worked Example
A man with a 38 cm neck, 85 cm waist and 178 cm height: waist minus neck is 47 cm, and the formula returns approximately 15.5% body fat — the "fitness" range. At 80 kg total weight that's about 12.4 kg of fat mass and 67.6 kg of lean mass.
How Accurate Is It?
Validation studies put the Navy method within about ±3–4 percentage points of DEXA scans for most people — comparable to consumer bioimpedance scales and decent calipers, without the equipment. It's least accurate for very muscular people (overestimates) and people with unusual fat distribution. Its real strength is tracking change: measured the same way at the same time of day, the trend over weeks is reliable even if the absolute number is a little off.
To act on your result, pair it with our calorie calculator for an energy target and our protein calculator to protect lean mass while cutting.
Frequently Asked Questions
Why does my smart scale show a different body fat number?
Bioimpedance scales send a small current through your body, and the reading swings with hydration, food, and recent exercise — daily fluctuations of 2–3 points are normal. The Navy method and a scale often disagree on the absolute number; pick one method and track its trend instead.
What's a realistic rate of body fat loss?
With a moderate calorie deficit and adequate protein, losing 0.5–1% of body fat per month is a strong, sustainable result. Faster drops usually reflect water loss or come at the cost of muscle.
Can I reduce fat in just my belly?
No — spot reduction doesn't work. Fat is mobilised body-wide according to genetics and hormones. A calorie deficit plus resistance training reduces total fat, and the belly shrinks as part of that process, often last.
Is some body fat necessary?
Yes. Essential fat (2–5% in men, 10–13% in women) is required for hormone production, organ protection and nerve function. Dropping below it is dangerous, and even sustained 'athlete' levels can disrupt hormones, sleep and recovery in some people.