Body Fat Calculator

How it's calculated

The main result uses the US Navy circumference method, which estimates body fat from height and tape measurements, using logarithms of the measurements in centimetres. For men it uses the waist minus the neck. For women it uses the waist plus the hip minus the neck. The formulas are:

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

As a second opinion the page also shows an estimate from BMI, age and sex: 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. The two methods often differ by a few percentage points, because the BMI formula cannot tell muscle from fat. Fat mass is your weight times the Navy percentage, and lean mass is the rest.

Reading the result

The category uses the American Council on Exercise ranges. For men these are essential fat up to about 5%, athletes 6 to 13%, fitness 14 to 17%, average 18 to 24%, and 25% or more in the obese range. For women the equivalents are up to about 13%, 14 to 20%, 21 to 24%, 25 to 31%, and 32% or more. Women need more essential fat than men, which is why their ranges sit higher.

These are estimates with a typical error of a few percentage points, and tape position changes the answer, so measure the same way each time and look at trends rather than single numbers. This tool is not a medical assessment. For a health concern, talk to a doctor. You can also use the BMI Calculator, the Lean Body Mass Calculator or the Ideal Weight Calculator alongside it.

Example

A 30-year-old man who is 178 cm tall and weighs 80 kg, with a 38 cm neck and 90 cm waist, gets about 20.1% from the Navy method, which falls in the average range. His BMI is 25.2, and the BMI-based estimate is about 21.0%.

Frequently asked

How accurate is the Navy body fat method?

It is an estimate, typically within a few percentage points of more precise methods such as DEXA scans. Accuracy depends on measuring in the right places, so measure the same way each time and follow trends rather than single readings.

Why are the Navy and BMI estimates different?

The Navy method uses body measurements, while the BMI method uses only weight, height, age and sex. BMI cannot separate muscle from fat, so it can overestimate for muscular people and underestimate for people with little muscle.

Where should I measure?

Measure the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hip at the widest point. Keep the tape snug but not tight and measure after breathing out normally.

What is a healthy body fat percentage?

Healthy ranges vary with age, sex and activity. Common fitness guides, such as the ACE ranges used here, put average men at about 18 to 24% and average women at about 25 to 31%. For personal advice, ask a doctor.

Is this suitable for children or during pregnancy?

No. The formulas are for healthy adults. They are not meant for under 18s, pregnant women, or anyone with a medical condition affecting body composition.