A tape-measure method
Neck, waist and, for the female formula, hips: no bioimpedance scale is needed for an estimate.
Health & wellness
Body fat calculator
Estimate body fat percentage with the U.S. Navy circumference method, with fat mass, lean body mass and a comparison with a BMI-based estimate.
Profile and measurements
Enter measurements taken with a tape measure. The main calculation uses the U.S. Navy circumference method.
Sex used by the formulas
Height
Measure just below the larynx without tightening the tape.
Measure horizontally at the narrowest point of the waist without pulling your stomach in.
For the female formula: measure around the widest part of the buttocks, keeping the tape horizontal.
Your estimated body composition
Estimated body fat percentage
%
U.S. Navy method
Fat mass
Lean body mass
Compare with the BMI-based estimate
BMI-based estimate
-
BMI
-
Difference between estimates
-
Both methods are statistical estimates. The difference illustrates the uncertainty of a calculation without a clinical body-composition measurement.
How to take the measurements
- Neck: just below the larynx, shoulders relaxed, without compressing the skin.
- Waist (female): at the narrowest point, with the tape parallel to the floor.
- Hips (female): around the widest part of the buttocks, with the tape parallel to the floor.
Method & sources
The main result uses U.S. Navy circumference equations: height, neck and abdominal circumference for men; height, neck, waist and hips for women. Weight is then used to convert the estimated percentage into fat mass and lean body mass. A second estimate based on BMI, age and sex uses the adult Deurenberg equation for comparison only.
Formula
U.S. Navy (measurements converted to inches) — Men: BF% = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76 · Women: BF% = 163.205 × log₁₀(waist + hips − neck) − 97.684 × log₁₀(height) − 78.387 · Adult Deurenberg: BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 male, 0 female)Limitations
- The U.S. Navy method estimates body composition from circumferences; it does not replace a clinical measurement such as DEXA.
- A few centimetres of difference when measuring the neck, waist or hips can change the result; always measure in the same way.
- The BMI-based estimate does not directly distinguish muscle from fat and may be less suitable for very muscular builds or extreme situations.
Was this tool useful?
How does this tool work?
Weight and BMI do not show how much of the body is fat. This calculator estimates body fat percentage from a simple tape measure using the U.S. Navy method, then converts that percentage into fat mass and lean body mass. A BMI-based estimate is shown separately to make clear that any formula remains an approximation.
Choose the sex used by the equations, enter your age, height and weight, then measure your neck and waist. For the female formula, add hip circumference. Metric, imperial and stone units are converted automatically before calculation.
The U.S. Navy method combines circumferences and height in a logarithmic equation. The resulting percentage is applied to weight to estimate fat mass and lean body mass.
The tool also calculates BMI and applies the adult Deurenberg equation. This second value should not be averaged with the Navy result: it compares two methods using different information.
How to use this tool
Enter your profile
Choose the sex used by the formulas, then enter age, height and weight.
Take your measurements
Measure neck and waist with a flexible tape; add hips for the female formula.
Compare without overinterpreting
Read the U.S. Navy estimate first, then use the difference from the BMI estimate as a reminder of uncertainty.
Good to know
Percentage translated into weight
The result also shows fat mass and lean body mass in kilograms or pounds.
Two estimates, no false precision
Navy remains the main method; the BMI estimate is shown alongside it to make differences between methods visible.
Understanding body fat calculations
Two approaches are shown separately: body circumferences and a statistical BMI-based estimate.
Fat mass
weight × body fat percentage ÷ 100
Lean body mass
weight − fat mass
Deurenberg
1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4
This tool provides an estimate for adults. It does not directly measure body fat and is not suitable during pregnancy, for people under 18 or for medical decisions.
Use cases
Estimate body fat percentage
Get an estimate from measurements you can take at home with a tape measure.
Separate fat and lean mass
Convert the estimated percentage into fat mass and lean body mass from your weight.
Compare two methods
Compare the circumference estimate with one derived from BMI, age and sex.
Tips and best practices
- Use a flexible tape against the skin without compressing it, and keep it horizontal for waist and hip measurements.
- To track change, measure under similar conditions and focus on the trend across several measurements rather than one isolated result.
- Do not confuse lean body mass with muscle mass: lean mass also includes water, bones, organs and other tissues.
Frequently asked questions
How can I calculate body fat without a special scale?
The U.S. Navy method uses a tape measure: height, neck and waist, plus hips for the female formula. These measurements provide an estimate of body fat percentage.
Why is weight required if the Navy formula mainly uses circumferences?
Weight is not needed for the Navy percentage itself. Here it converts that percentage into fat and lean mass and calculates BMI for the Deurenberg comparison.
Why are the Navy and BMI estimates different?
They use different information. Navy uses body circumferences; Deurenberg uses BMI, age and sex. A difference is therefore normal and underlines that both are estimates.
Is lean body mass the same as muscle?
No. Lean body mass is everything that is not fat: muscles, water, bones, organs and other tissues.
Can I use this calculator during pregnancy?
No. Pregnancy-related changes in weight, measurements and body composition make these equations unsuitable.
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