Two people can weigh the same and have the same BMI while carrying very different amounts of fat. Body fat percentage describes the share of your weight that is fat tissue, which makes it a more direct measure of body composition than the scales. Laboratory tools such as DEXA scans and underwater weighing measure it accurately but are costly and not widely available, so this calculator offers two estimates that need only a tape measure or a scale: the United States Navy circumference method and the Deurenberg formula based on BMI.
Both are estimates. Treat them as a way to track change over time with the same method, not as a precise measurement.
How to use the body fat calculator
- Choose your sex, because fat distribution and the equations differ for men and women.
- Select a method. The Navy method uses neck, waist and, for women, hip circumference. The BMI method uses age instead.
- Enter your height and weight. Weight gives the fat and lean mass in kilograms or pounds.
- Enter the tape measurements in centimetres or inches. Measure twice and use the average.
- Read the estimate, its category and the split into fat and lean mass.
Body fat formulas
US Navy, women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
Deurenberg: %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women)
In the Navy equations all lengths are in inches. They were derived by Hodgdon and Beckett at the Naval Health Research Center (reports 84-29 and 84-11, 1984) and appear in US Department of Defense body-composition rules. The Deurenberg formula comes from Deurenberg, Weststrate and Seidell, British Journal of Nutrition 1991;65:105–114.
Fat mass is weight × %BF ÷ 100, and lean mass is weight minus fat mass.
Worked example
A man is 178 cm (70.08 in) tall, weighs 80 kg, with a neck of 38 cm (14.96 in) and a waist of 86 cm (33.86 in).
- Waist − neck = 33.86 − 14.96 = 18.90 in; log10 = 1.2765
- log10 of height = log10(70.08) = 1.8456
- %BF = 86.010 × 1.2765 − 70.041 × 1.8456 + 36.76 = 17.3%
- Fat mass = 80 × 17.3% = 13.8 kg; lean mass = 66.2 kg
With the BMI method the same man at age 35 has BMI 25.2, so %BF = 1.20 × 25.2 + 0.23 × 35 − 10.8 − 5.4 = 22.1%. The two methods answer a little differently, which is why one method should be kept for tracking.
Body fat categories
The American Council on Exercise (ACE) publishes the ranges below. They are descriptive guides for adults, not medical thresholds.
| Category (ACE) | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
What the percentage means in kilograms
Fat and lean mass for common body weights at three body-fat levels, calculated from weight × percentage.
| Body weight | At 15% body fat | At 25% body fat | At 35% body fat |
|---|---|---|---|
| 60 kg | 9.0 kg fat / 51.0 kg lean | 15.0 kg fat / 45.0 kg lean | 21.0 kg fat / 39.0 kg lean |
| 70 kg | 10.5 kg fat / 59.5 kg lean | 17.5 kg fat / 52.5 kg lean | 24.5 kg fat / 45.5 kg lean |
| 80 kg | 12.0 kg fat / 68.0 kg lean | 20.0 kg fat / 60.0 kg lean | 28.0 kg fat / 52.0 kg lean |
| 90 kg | 13.5 kg fat / 76.5 kg lean | 22.5 kg fat / 67.5 kg lean | 31.5 kg fat / 58.5 kg lean |
Getting reliable measurements
- Use a flexible, non-stretch tape held level around the body without compressing the skin.
- Measure at the same time of day, ideally in the morning before eating, because meals and hydration shift the waist reading.
- Take each measurement two or three times and use the average; a 1 cm error in the waist can move the result by about 1 percentage point.
- Stay with one method. Comparing a Navy result from this month with a BMI-method result from last month tells you nothing.
Limits
The Navy method assumes a typical body shape, so it can be off for people with unusually large or small necks, thick thighs or very muscular builds. The BMI method cannot distinguish muscle from fat. Neither is validated for pregnancy, children or people with oedema. For a precise number a DEXA scan or other clinical assessment is the standard. Ask a clinician about any result that worries you; this page is for information only and is not medical advice.
Related tools: the Navy Body Fat Calculator focuses on the tape method, the Lean Body Mass Calculator estimates muscle and organ mass, the BMI Calculator shows the weight-for-height screen and the Waist-to-Height Ratio Calculator tracks abdominal fat.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center Reports 84-29 and 84-11, 1984.
- US Department of Defense Instruction 1308.3, Physical Fitness/Body Composition Program Procedures.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr 1991;65:105–114.
- American Council on Exercise. What Are the Guidelines for Percentage of Body Fat Loss? (body fat categories).
Frequently asked questions
How accurate is the Navy body fat method?
It was developed by Hodgdon and Beckett for the US Navy as a quick screening tool and is reasonably close to hydrostatic weighing for groups of people, but individual errors of several percentage points are normal. It works best for average builds and can mislead for very muscular or very lean people.
Where do I measure my neck, waist and hips?
Measure the neck just below the larynx, sloping slightly down at the front. For men, measure the waist level with the navel; for women, at the narrowest point of the torso. Measure the hips at their widest point. Keep the tape snug but not tight, breathe out naturally and take each measurement twice.
Why is the BMI method less precise?
The Deurenberg equation estimates fat from BMI, age and sex only, so it cannot see muscle. A muscular person will be overestimated and an older person with little muscle may be underestimated. It is best used when you cannot take tape measurements.
What is a healthy body fat percentage?
There is no single healthy number. The American Council on Exercise lists essential fat at 10–13 percent for women and 2–5 percent for men, with an average range of 25–31 percent for women and 18–24 percent for men. Health risks depend on much more than the percentage alone, so ask a clinician about your own situation.
Is body fat more useful than BMI?
Body fat describes composition, which BMI cannot, but it is harder to measure accurately at home. Many people find it useful to track both, plus waist size, rather than relying on one number. See the BMI Calculator to compare.