Free tool
Navy body fat calculator
A more useful number than BMI, because it separates muscle from fat. This uses the US Navy circumference method: a tape measure and three measurements, no calipers needed.
Updated
How to measure
Neck: just below the larynx, tape sloping slightly down at the front. Do not flex.
Waist: at the navel for men, at the narrowest point for women. Relaxed, at the end of a normal breath out. Do not suck in.
Hip: women only, at the widest point.
Measure first thing in the morning, before eating, and keep the same routine every time. The absolute number matters less than the direction it moves over a month.
Reference
What the ranges mean.
Women carry more essential fat than men. It is physiological, not a fitness gap. Anything at or below the essential band is not a target; it is a medical concern.
Expect the Navy method to be within roughly 3–4 percentage points of a DEXA scan for most people. It is far better at tracking change than at nailing an absolute figure.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
The US Navy body fat formula
The method was developed by the US Navy in the 1980s to screen personnel without specialist equipment. It uses the fact that fat is stored around the waist and hips, while the neck stays relatively constant, to estimate body density from circumferences. All measurements are in centimetres.
| Sex | Body fat % |
|---|---|
| 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 |
Because it depends on a few centimetres of tape, a 1 cm error in the waist moves the result by about one percentage point. Measure the same way every time and the trend will be reliable even when the absolute figure is not. The Navy formula explained →
Body fat percentage vs BMI
BMI only knows your height and weight, so a muscular person and a sedentary person of the same size get the same number. Body fat percentage separates the two. That makes it the better number to track during weight loss, where the goal is to lose fat while keeping muscle. The scale can stall for a fortnight while your waist keeps shrinking.
If you want a single quick screen with even less measuring, waist-to-height ratio is close to body fat in how well it predicts health risk.
Frequently asked questions
How accurate is the US Navy method?
Usually within 3–4 percentage points of a DEXA scan. It is less accurate at the extremes (very lean or very heavy), but it is free, repeatable and good at showing direction over time, which is what actually matters.
Why does it ask for my waist rather than my weight?
Because circumference is what correlates with fat distribution. Weight cannot distinguish muscle from fat; a waist measurement largely can. Weight is only used here to convert the percentage into fat and lean mass.
My result looks wrong.
Check that everything is in centimetres and that waist is larger than neck. The formula breaks down if the difference between them is very small, in which case the calculator will tell you to re-measure rather than print a nonsense figure.
How fast can body fat realistically drop?
Roughly half a percentage point to one point a month at a sensible deficit. Anything much faster usually means muscle is going too. Use the calorie deficit calculator to set a rate you can hold.
Next step
Measuring is easy. Logging is the hard part.
Free to start on iPhone and Android.
