Health · Body Fat

Body Fat Calculator

A tape measure is all you need — and it catches what BMI misses.

Reading your result

Fill in every field and the steps will be spelled out here.

How it is calculated

US Navy method Men = 495 ÷ (1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450 Women = 495 ÷ (1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.22100×log₁₀(height)) − 450 Lean mass = weight × (1 − body fat %)

This covers ground BMI cannot. Height and weight alone cannot tell a muscular frame from a soft one, which is why BMI over-reads trained bodies and under-reads low-muscle ones. Circumference brings in where the fat actually sits, and most of that error goes away.

A tape measure beats a smart scale for consistency. Bioimpedance scales read differently depending on hydration — after a workout or a large drink the number moves without your body having changed. Tape measurements do not have that problem, so for tracking change over weeks they are the steadier instrument.

Trend matters more than the absolute number. Any formula of this kind can be a few percentage points off. Measured the same way each week, though, the direction is reliable — and a waist shrinking while weight holds steady is exactly what recomposition looks like.

Technique decides the number. Pulling the tape tight reads low, leaving it slack reads high. Exhale, rest the tape against the skin without compressing it, and return to the same landmarks every time.

Frequently asked questions

Why does this differ from my smart scale?

They measure different things. Bioimpedance infers fat from electrical resistance and is sensitive to hydration; this formula infers it from circumference. Neither is definitive — pick one method and stay with it.

Is lower always better?

No. Roughly 3–5% in men and 10–13% in women is essential fat required for normal function. Below that, hormonal and immune problems follow. The athlete range is also difficult to hold and rarely worth holding.

Where exactly do I measure?

Men: waist at the navel. Women: waist at its narrowest and hip at its widest. Neck just below the larynx for both. Consistency between measurements matters more than pinpoint accuracy.