Body Fat Calculator — Free Online Tool
You don't need a lab to estimate body fat. The US Navy method uses a tape measure and three circumferences to estimate your body-fat percentage within a few points of high-tech methods.
What is the Body Fat Calculator?
Scales tell you total weight, but not composition — two people at 180 lbs can carry very different amounts of fat. The US Navy body-fat formula, developed from circumference measurements of service members, predicts body fat from height, neck, waist (and hip for women) with surprising accuracy for a tape-measure method — typically within 3–4% of DEXA scans.
Why these spots? Neck size reflects lean mass; waist (and hip) reflect fat storage. The logarithmic formula weights them accordingly. For best results, measure in the morning, on bare skin, with the tape snug but not compressing — and measure waist at the navel, the Navy's specified site.
How to use this calculator
- Select your sex (formulas differ).
- Enter height, neck, waist in cm (plus hip for women) and your weight.
- Click Calculate Body Fat for your % and category.
Formula
Frequently asked questions
How accurate is the Navy body fat method?
Within about 3–4% of DEXA for most people — excellent for tracking trends, though not lab-grade.
Where exactly do I measure my waist?
At the navel (belly button), horizontal, after exhaling normally. That's the Navy's specified site.
Why does the women's formula need hips?
Fat distribution differs by sex; hip circumference significantly improves the estimate for women.
What is a healthy body fat percentage?
Roughly 10–20% for men and 18–28% for women is considered healthy/fit; athletes run lower.