Body Fat Calculator
Weight Doesn't Tell You What You're Made Of
Two people at the same height and weight can have completely different amounts of fat versus muscle, and neither BMI nor the bathroom scale can tell them apart. The U.S. Navy circumference method sidesteps that problem by measuring the shape of the body directly — neck, waist, and (for women) hip — and running those numbers through a formula validated against underwater weighing, the gold-standard lab method.
The Formula
Body Fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(Waist − Neck) + 0.15456 × log₁₀(Height)) − 450
Women:
Body Fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(Waist + Hip − Neck) + 0.22100 × log₁₀(Height)) − 450
All measurements are in centimeters (imperial inputs are converted automatically). The formula was developed by the U.S. Navy in the 1980s as a fast, equipment-free alternative to hydrostatic weighing for fitness testing.
Body Fat Percentage Categories
| Category | Men | Women |
|---|---|---|
| Essential Fat | Below 6% | Below 14% |
| Athletic | 6% – 13.9% | 14% – 20.9% |
| Fitness | 14% – 17.9% | 21% – 24.9% |
| Acceptable | 18% – 24.9% | 25% – 31.9% |
| Obese | 25% and above | 32% and above |
Why the Circumference Method Holds Up
- No special equipment — a tape measure gets you a research-backed estimate that calipers or bioelectrical scales often can't match in accuracy without training.
- Tracking body recomposition — measuring waist and neck monthly shows fat loss trends even when total weight barely moves, which happens often during resistance training.
- Screening beyond BMI — useful for distinguishing a muscular, high-BMI individual from someone carrying excess fat at the same BMI.
How to Use This Calculator
- Choose Metric (cm) or Imperial (in) units.
- Select Male or Female — selecting Female adds a Hip Circumference field.
- Enter your Height.
- Enter your Neck Circumference and Waist Circumference (and Hip Circumference if applicable).
- Select Calculate to get your estimated body fat percentage and category.
Related Calculations
Cross-check the result against the Lean Body Mass Calculator, or look at fat distribution risk with the Waist to Hip Ratio Calculator.