Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy tape method.
Results update as you type.
About this calculator
This calculator estimates body fat percentage using the U.S. Navy circumference method, which needs only a tape measure. It feeds your height, neck and waist measurements — plus hip for women — into the Navy formula, which uses the ratio between these circumferences to estimate how much of your body is fat. Enter your weight too and it also splits that into fat mass and lean body mass.
For example, a man 175 cm tall with a 38 cm neck and an 85 cm waist comes out at roughly 17% body fat, which sits in the fitness range. Measuring accurately matters: keep the tape snug but not compressing the skin, take the waist at the navel and the neck just below the larynx.
Use it as a free, at-home alternative to calipers or a DEXA scan for tracking fat loss or muscle gain over weeks and months. It is an estimate, typically within a few percent of a lab measurement, so focus on the trend between measurements rather than any single reading.
Frequently asked questions
How accurate is the Navy method?
It is typically within about 3-4% of a DEXA scan for most people. Accuracy depends on measuring at the right spots with the tape snug but not compressing the skin.
What is a healthy body fat percentage?
General fitness ranges are roughly 14-24% for men and 21-31% for women, but healthy ranges vary with age and athletic goals.
Where exactly do I measure?
Measure the neck just below the larynx, the waist horizontally at the navel (at the narrowest point for women), and for women the hips at the widest point. Keep the tape level and snug without compressing the skin for the most reliable result.
Why do women need a hip measurement?
The Navy formula for women uses waist, neck, hip and height together, because women’s fat distribution differs from men’s. The men’s formula uses only waist, neck and height, so the hip field is required for women and ignored for men.
How is body fat percentage different from BMI?
BMI is only a weight-to-height ratio and cannot tell fat from muscle, whereas the Navy method estimates the actual proportion of fat using body measurements. Two people with the same BMI can have very different body fat percentages.
What are fat mass and lean body mass?
Fat mass is your body fat percentage applied to your weight; lean body mass is everything else — muscle, bone, organs and water. Enter your weight under advanced options and the calculator reports both.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/body-fat/curl
curl "https://calculator.free/api/v1/body-fat/?sex=male&units=metric&height=175&neck=38&waist=85"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/body-fat/?" + new URLSearchParams({
"sex": "male",
"units": "metric",
"height": "175",
"neck": "38",
"waist": "85"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.