Waist to Height Ratio
The measure BMI structurally cannot give you.
Health & Home
Body Fat Calculator
US Navy tape method, with its real margin of error.
What it does. The US Navy method estimates body fat from height and a few circumference measurements. It is accurate to roughly 3 to 4 percentage points against a DEXA scan — good enough to track a direction over months, not precise enough to argue about a single point.
Runs in your browserNothing uploadsNo signupWorks offline
How to use Body Fat Calculator
- Measure neck and waist (and hips, for women) with a soft tape.
- Enter them with your height.
- Read the estimate, the range around it, and your lean mass.
How to measure so the number means something
- Same time of day — first thing, before eating or drinking. Waist changes measurably through the day.
- Tape snug, not tight — it should sit flat without compressing the skin.
- Neck — just below the larynx, tape sloping slightly down at the front.
- Waist — at the navel for men, at the narrowest point for women.
- Hips — at the widest point, feet together.
- Do not hold your breath or brace — breathe out normally and relax.
Consistency matters more than precision. A measurement taken the same wrong way every time still tracks change correctly; one taken differently each time tracks nothing.
How the methods compare
| Method | Typical error | Practicality |
|---|---|---|
| DEXA scan | ±1–2% | Clinic, costs money |
| Hydrostatic weighing | ±2% | Rare, specialist facility |
| Skinfold calipers | ±3–4% | Cheap, needs a trained hand |
| Navy tape method | ±3–4% | Tape measure, two minutes |
| Bioimpedance scales | ±4–8% | Instant, moves with hydration |
Bioimpedance scales are the ones to be careful with. They pass a current through the body and infer composition from resistance, so hydration, a recent meal or a workout can shift the reading by several points with no change in body composition.
What counts as a healthy range
Essential fat — the minimum for normal function — is around 3 to 5% for men and 10 to 13% for women. The difference is physiological, not a matter of fitness.
Typical fitness ranges run roughly 14 to 20% for men and 21 to 28% for women, with athletes lower.
Very low body fat is not a health goal in itself. Sustained low levels are associated with hormonal disruption, bone loss and menstrual dysfunction, and the point at which that starts differs between people.
Frequently asked questions
How accurate is the Navy body fat method?
About 3 to 4 percentage points against a DEXA scan — comparable to skinfold calipers. It tracks direction over months well; it is not precise enough to argue about a single point.
Why do my smart scales disagree?
Bioimpedance infers composition from electrical resistance, so hydration, a recent meal or a workout can move it several points with no real change. Weigh under identical conditions if you use one.
What is a healthy body fat percentage?
Roughly 14 to 20% for men and 21 to 28% for women as typical fitness ranges. Essential fat — the physiological minimum — is about 3 to 5% and 10 to 13% respectively.
Why does the formula ask for different measurements for men and women?
Because fat distribution differs, and the equation was fitted separately for each. The women's version includes hip circumference to capture that.
How often should I measure?
Every two to four weeks. Within the method's margin of error, weekly changes are mostly noise, and measuring more often mainly produces frustration.