📏 Body Fat Percentage Calculator
The U.S. Navy method estimates body fat from a few tape measurements, neck, waist (and hip for women) plus height. Enter your values below, results update instantly, entirely on your device.
U.S. Navy circumference method (fitness)
How the body fat percentage calculator works
U.S. Navy method (log₁₀, measurements in cm). Men: 495 ÷ (1.0324 − 0.19077·log(waist − neck) + 0.15456·log(height)) − 450. Women add the hip and use different constants. Measure the waist at the navel and the neck below the larynx. Once you have the percentage, fat mass = body weight × body fat % and lean mass is the remainder, so an 80 kg person at 20% carries 16 kg of fat and 64 kg of lean mass.
Example: A man 175 cm tall with a 38 cm neck and 85 cm waist estimates at roughly 18% body fat.
The tape method is convenient but approximate, expect ±3-4% versus a DEXA scan, and it can mis-estimate very lean or very heavy builds. Measure relaxed (don't suck in), snug but not compressing, and take each measurement twice. General fitness categories: for men, ~6-13% athletic, 14-17% fitness, 18-24% average; women run ~8% higher. Not medical advice.
Frequently asked questions
How does the U.S. Navy body fat method work?
It estimates body fat from body-circumference measurements, neck and waist for men, plus hips for women, together with height, using a formula the U.S. Navy validated against more precise methods. No calipers or scales needed, just a tape measure.
How accurate is the tape-measure method?
Reasonably, for tracking trends: typically within 3-4 percentage points of a DEXA scan. It's less accurate at the extremes (very lean or very high body fat). Consistency matters more than absolute accuracy, measure the same way each time.
Where exactly do I measure?
Neck: just below the larynx, tape sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women. Hips (women): at the widest point. Stand relaxed and breathe normally, don't suck in.
What is a healthy body fat percentage?
Rough guides: men 10-20% and women 18-28% are commonly considered healthy, with athletes lower. Essential fat (the minimum) is about 3-5% for men and 10-13% for women. These are general ranges, not medical thresholds.
How do I turn a body fat percentage into fat mass?
Multiply your weight by the percentage as a decimal: 75 kg at 18% is 75 × 0.18 = 13.5 kg of fat, leaving 61.5 kg of lean mass. Watching lean mass helps confirm you are losing fat rather than muscle.
Why do men and women use different formulas?
Women naturally carry more essential fat and store it differently, so the Navy method adds the hip measurement and uses separate constants for women to keep the estimate accurate.
Is this body fat percentage calculator accurate and private?
Yes. It uses the standard published formula, shows its working under every result, and computes locally in your browser, your inputs are never sent to a server, and the page works offline.