What a body fat calculator does
A body fat calculator estimates what share of your weight is fat. You only need a tape measure: your height, your neck, your waist and, for women, your hip. It then gives your body fat percentage, your fat mass and your lean mass.
It helps people who follow their fitness and want more than the scale or the BMI can tell them, since two people of the same weight can have very different amounts of fat.
The result is an estimate for information only. It is not a medical measurement, and a health professional can interpret it for you.
How to use this calculator
- You are: choose man or woman, because the formula is different for each.
- Age, Height, Weight: your age in years, your height in centimetres and your weight in kilograms.
- Neck: measure just below the Adam's apple, with the tape level, in centimetres.
- Waist: measure at the navel without pulling in your stomach, in centimetres.
- Hip: asked for women only. Measure at the widest point, in centimetres.
Measure in the morning, on bare skin, and take the average of two tries. The result shows your body fat, your fat mass, your lean mass and your category.
The US Navy formula
The calculator uses the US Navy method, built from tape measurements and published by Hodgdon and Beckett in 1984. All sizes are in centimetres:
Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- log10 is the base-10 logarithm, a button on any scientific calculator.
- For men the formula uses the waist minus the neck. For women it uses waist plus hip minus the neck.
- Fat mass is your weight × the percentage ÷ 100. Lean mass is your weight minus the fat mass.
Your age is not in the formula. It is only used to check that the adult ranges apply.
Worked example
A woman, 30 years old, 165 cm, 62 kg, neck 33 cm, waist 72 cm, hip 96 cm.
- Waist + hip − neck: 72 + 96 − 33 = 135.
- Logarithms: log10(135) = 2.1303 and log10(165) = 2.2175.
- Denominator: 1.29579 − 0.35004 × 2.1303 + 0.22100 × 2.2175 = 1.0402.
- Percentage: 495 ÷ 1.0402 = 475.89, then 475.89 − 450 = 25.89, so 25.9%.
- Fat mass: 62 × 25.89 ÷ 100 = 16.1 kg. Lean mass: 62 − 16.1 = 45.9 kg.
- Category: 25.9% falls in the 25% to 31.9% band for women, called Average.
Her body fat is 25.9%, which is 16.1 kg of fat and 45.9 kg of lean mass, in the Average category.
Try the same measurements in the calculator above to see the same result.
Key concepts
Fat mass and lean mass
Fat mass is the weight of fat in your body. Lean mass is everything else: muscle, bones, organs and water. Two people with the same weight can have very different fat mass.
The categories
The calculator uses ACE ranges: Essential, Athletes, Fitness, Average and Obese. For women they are 10 to 13%, 14 to 20%, 21 to 24%, 25 to 31% and 32% and above. For men they are 2 to 5%, 6 to 13%, 14 to 17%, 18 to 24% and 25% and above.
Essential fat
Your body needs some fat to work. It protects organs and helps hormones. Very low percentages are not a goal, and a doctor should guide anyone in that range.
Body fat or BMI
BMI only compares weight with height. Body fat looks at the fat itself, so it says more about build. Neither is a diagnosis.
Tips for measuring well
- Be precise with the tape. For the woman in the example, a waist of 70 cm gives 24.9% and 74 cm gives 26.9%. Two centimetres move the result by about one point.
- Keep the tape level and snug, not tight. Measure twice and use the average.
- Measure under the same conditions each time, for example in the morning before eating, to follow your progress.
- A man of 35 years, 180 cm, 80 kg, with a neck of 38 cm and a waist of 90 cm gets 19.8%. At a waist of 86 cm he gets 16.9%.
- Do not aim for the lowest number. Talk to a doctor before a strict diet or training plan, and do not use these measurements during pregnancy.
Frequently asked questions
How accurate is the tape measure method?
It is an estimate. Lab scans are more precise, and a small error in the tape changes the result. Use it to follow your own trend more than to compare yourself with others.
Is body fat better than BMI?
It says more, because BMI cannot tell muscle from fat. To see both, calculate your BMI too. Neither replaces medical advice.
What is a healthy body fat percentage?
There is no single healthy number, because it depends on sex, age and build. The bands listed above show where your result falls. A doctor can tell you what suits you.
How can I lower my body fat?
This page cannot give a personal plan. In general, regular activity and balanced meals are the base. You can estimate your daily energy needs with the calorie calculator, and ask a doctor or dietitian before changing your diet.
Can I use it during pregnancy?
No. The measurements are not reliable in pregnancy. You can estimate your due date with the due date calculator and ask your doctor about healthy weight gain.