Body Fat Calculator

Bathroom scales tell you what you weigh, not what that weight is made of. This calculator estimates how much of you is fat using the US Navy method: a formula built from your height and a few tape measurements (neck and waist, plus hips for women). It was developed by the US Navy to check fitness without lab equipment, and for most adults it lands within about 3–4 percentage points of a lab scan.

You get your body fat percentage on a coloured scale, the category it falls in from the American Council on Exercise table (essential fat, athletes, fitness, average and obese, with different ranges for men and women), and, if you add your weight, how many kilograms or pounds are fat and how many are lean mass. A second, rougher estimate from your BMI and age sits beside it, clearly labelled, so you can see how much the tape adds.

There is a drawing showing exactly where to put the tape, because a centimetre in the wrong place moves the answer. Everything is worked out in your browser: your measurements are never uploaded or stored.

1. Choose Female or Male, and “cm · kg” or “in · lb”. Values convert when you switch units.
2. Measure your neck and waist (and hips for women) following “How to measure”, then type them with your height.
3. Add your weight to see fat mass and lean mass, and your age for the BMI-based estimate.
4. Read your body fat percentage, its category and where you sit on the scale.
5. Tap “Copy results” to keep a note, and measure again in four to six weeks to see the trend.

• US Navy circumference formula for men (neck and waist) and women (neck, waist and hips).
• Metric or imperial measurements, with feet and inches for height and automatic conversion when you switch.
• Body fat category from the American Council on Exercise table, with separate ranges for men and women.
• A coloured scale with a marker, plus a labelled list of every band with yours marked “You”, so nothing relies on colour alone.
• Fat mass and lean mass from your weight, and the weight you would reach at the top of the “Fitness” band with the same lean mass.
• A second estimate from BMI, age and sex (Deurenberg formula), labelled as rougher.
• A how-to-measure drawing that changes for men and women, and plain warnings when a measurement looks wrong.

• Measure first thing in the morning, before eating or exercising, and always in the same spots. Small changes in where the tape sits change the result more than a week of eating well.
• Don’t breathe in or pull your stomach in for the waist. Stand relaxed, breathe out normally, then read the tape.
• Use a soft, non-stretch tape. Old fabric tapes stretch; a cheap fibreglass one stays true.
• Track the trend, not one reading. If your waist shrinks while your weight stays the same, you are probably losing fat and keeping muscle.
• Very muscular necks (common in rugby players and wrestlers) can make the Navy method read low. A DEXA scan is the gold standard if you need precision.