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Free online body fat percentage calculator

Body fat percentage measures how much of your weight is fat versus lean mass. This calculator uses the US Navy circumference method — a tape measure is all you need.

Sex
Units
Body fat percentage
—
Fat mass
—
lb
Lean mass
—
lb
About this calculator

How to use

  1. Select your sex and preferred unit system with the toggles.
  2. Enter height, neck circumference, waist circumference, and (for women) hip circumference.
  3. Enter your body weight to get fat mass and lean mass in pounds.
  4. Results show body fat percentage, fat mass, lean mass, and fitness category.

The formula

Men (US Navy):

BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

Women (US Navy):

BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

All measurements in inches. Metric values are converted before applying the formula.

Fat mass and lean mass are derived from body weight:

Fat mass  = weight × (BF% / 100)
Lean mass = weight − fat mass

Worked example

Male, 5 ft 10 in (70 in), neck 15 in, waist 32 in, weight 180 lb:

  • Waist − neck = 17
  • log10(17) ≈ 1.2304; log10(70) ≈ 1.8451
  • BF% = 86.010 × 1.2304 − 70.041 × 1.8451 + 36.76 ≈ 14.7% (Fitness category)
  • Fat mass: 180 × 0.147 ≈ 26.5 lb
  • Lean mass: 180 − 26.5 ≈ 153.5 lb

Notes

Health disclaimer: Results are statistical estimates based on population-level equations, not clinical measurements. Body fat percentage can vary by several percentage points from lab methods like DEXA or hydrostatic weighing. Do not use these results to diagnose or treat any medical condition. Consult a qualified healthcare professional for personalized health guidance.

  • Source: Hodgdon JA & Beckett MB (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center.
  • Category thresholds: American Council on Exercise (ACE).

Frequently asked

How is body fat percentage calculated here?
This calculator uses the US Navy circumference method, developed by Hodgdon and Beckett (1984). For men: BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All measurements in inches.
What are healthy body fat ranges?
For men: Essential fat 2–5%, Athletic 6–13%, Fitness 14–17%, Average 18–24%, Obese 25%+. For women: Essential fat 10–13%, Athletic 14–20%, Fitness 21–24%, Average 25–31%, Obese 32%+. These ranges are from the American Council on Exercise (ACE).
How accurate is the Navy method?
The US Navy circumference method predicts body fat within about 3–4 percentage points compared to DEXA scans for most healthy adults. It is less accurate at extreme body compositions and for very muscular individuals. It is a practical screening tool, not a clinical measurement.
Why do male and female categories differ?
Women naturally carry more essential fat — approximately 10–13% versus 2–5% for men — due to hormonal and physiological differences including reproductive function. The category thresholds reflect these biological differences.
How do I measure neck, waist, and hip correctly?
Neck: measure just below the larynx (Adam's apple), keeping the tape horizontal. Waist (men): measure at the navel level at the widest point of the abdomen. Waist (women): measure at the narrowest point of the torso. Hip (women only): measure at the widest point around the hips and buttocks. Stand straight, breathe normally, and do not suck in.