Body Fat Calculator

It’s a reasonable estimate — typically within a few percentage points of a DEXA scan for average builds — but it’s not a precise measurement. It infers fat from circumferences, so unusual proportions can throw it off. Use it for trends, not as a clinical figure.

Use a flexible tape, relaxed and not compressing the skin. Neck: below the larynx. Waist: at the navel for men, at the narrowest point for women. Hip (women): at the widest point. Measure on bare skin, breathing normally, for consistency.

The Navy equations were fitted separately by sex. Women’s formula includes the hip because fat distribution and the waist-to-hip relationship differ, which improves the estimate. Men’s formula uses only neck and waist.

It varies by sex and goals. Rough ACE guides: for men, 14–17% is “fitness” and 18–24% “average”; for women, 21–24% is “fitness” and 25–31% “average”. Some fat is essential — very low levels carry their own risks.

Fat mass is your weight multiplied by body-fat percentage; lean mass is everything else — muscle, bone, organs, water. The tool shows both when you enter your weight, which is handy for judging whether weight change is fat or muscle.

For body composition, usually yes — it estimates fat directly rather than inferring from weight and height, so it isn’t fooled by muscle the way BMI is. But it needs careful measuring, and both are estimates. They complement each other.

The formula needs the waist to be larger than the neck (and, for women, waist plus hip larger than the neck). If not, or if a value is outside a plausible range, the estimate can’t be computed — re-check your tape readings.

Yes. Everything is computed in your browser; nothing is uploaded and analytics never receives your measurements.