Body Fat Percentage Calculator (US Navy Method)
This free body fat calculator estimates body fat percentage with the US Navy circumference method. Enter height, neck, and waist measurements (plus hip for women) and get body fat percentage, fat mass, and lean body mass. Metric and imperial units are supported, and everything runs in your browser.
The Navy Method is a practical tape-measure estimate: it does not require special equipment, and it is consistent enough to track change over time when you measure the same way each time. It is a screening estimate, not a clinical body-composition test.
How the Navy Method Works
The formula uses the relationship between circumference measurements and height to approximate body density, then converts density to a body fat percentage. Men measure neck and waist; women also measure hips. The calculator shows fat mass and lean body mass in your chosen units, with BMI shown for context.
How to Measure Correctly
- Waist: measure at the navel for men, at the narrowest point for women, without pulling the tape tight.
- Neck: measure just below the larynx, with the tape sloping slightly downward at the front.
- Hips (women): measure at the widest point.
- Consistency: measure at the same time of day, relaxed, and repeat each measurement twice.
BMI vs Body Fat Percentage
BMI is a weight-to-height index and cannot distinguish fat from muscle. Body fat percentage estimates composition, which is usually more informative for fitness planning. Use both as trend indicators: recalculate every 4 to 8 weeks, and adjust calorie and macro targets from the trend rather than a single reading.