Body Composition Check
Estimate your BMI, waist-to-height ratio and body fat percentage using the US Navy tape method — plus an honest note on what these numbers can and cannot tell you.
At the narrowest point for women, at the navel for men. Relaxed, not held in.
Just below the larynx, tape sloping slightly down at the front.
How this is worked out
BMI is weight divided by height squared, banded to the WHO/NHS categories. It is a population screening tool and cannot distinguish muscle from fat, so a well-trained athlete will often read “overweight” on it and be nothing of the sort.
Waist-to-height ratio is the better single number for most people, and is what NICE recommends: keep your waist under half your height. It works across different builds and ages, and tracks central fat, which is the part that matters for health risk.
Body fat uses the US Navy circumference method. On a group it is accurate to roughly ±3–4 percentage points against a DEXA scan, and it is sensitive to how you hold the tape. Its real value is as a trend: measure the same way, at the same time of day, every few weeks, and watch the direction rather than the absolute figure.
Information only — not medical advice. These are estimates from population-level formulas, not a substitute for professional assessment. See our full disclaimer.