Body Fat Calculator: US Navy, BMI and Army Methods
Estimate body fat percentage with the US Navy tape method, a BMI-based formula or the US Army 2023 one-site tape test, in metric or US units. Shows fat mass, lean mass and the ACE category. Nothing is uploaded.
Enter your measurements to see your body fat estimate.
About the Body Fat Calculator
The Body Fat Calculator estimates what share of your body weight is fat. It offers three published methods: the US Navy tape method, which uses a few circumference measurements and your height; a BMI-based estimate, which needs only weight, height, age and sex; and the US Army 2023 one-site tape test, which uses your weight and a single abdominal measurement. Each result shows the body fat percentage, the fat mass and lean mass in kilograms or pounds, and the matching category from the American Council on Exercise (ACE) chart.
You can enter measurements in metric units (kilograms and centimetres) or in US customary units (pounds and inches). The calculator uses the published centimetre form of the Navy formula for metric input and the published inch form for US input, so the two can differ by a fraction of a percentage point.
This is an estimate, not medical advice. Tape and BMI formulas predict an average for people with your measurements, and an individual result can be several percentage points away from a laboratory method such as a DEXA scan or underwater weighing.
How to measure
Steps
- Choose a method: US Navy tape, From BMI or US Army 2023.
- Choose your sex and your units.
- Enter each measurement. Results appear as soon as every field holds a valid number.
Tape positions
Measure the neck just below the larynx, with the tape sloping slightly down to the front. Measure the waist horizontally at the level of the navel after breathing out normally. For women, measure the hips at the widest point of the buttocks. Keep the tape snug but not pressing into the skin, and take each measurement two or three times.
The formulas
The US Navy method comes from Hodgdon and Beckett (1984). With every measurement in inches:
The centimetre form predicts body density and converts it to body fat with the Siri equation. For women the constants are 1.29579, 0.35004 and 0.22100, applied to waist plus hip minus neck:
The BMI-based estimate is the adult formula of Deurenberg, Weststrate and Seidell (1991), with sex 1 for men and 0 for women:
It is less precise than the tape method because BMI cannot tell muscle from fat.
ACE body fat categories
The calculator names the band your estimate falls in:
- Essential fat: women 10–13 %, men 2–5 %.
- Athletes: women 14–20 %, men 6–13 %.
- Fitness: women 21–24 %, men 14–17 %.
- Average: women 25–31 %, men 18–24 %.
- Obese: women 32 % and over, men 25 % and over.
Worked example
A man who weighs 80 kg and is 178 cm tall, with a 90 cm waist and a 38 cm neck, gets 20.1 % body fat by the Navy method. That is 16.1 kg of fat mass and 63.9 kg of lean mass, in the ACE "Average" band.
Army standard
The Army Body Fat Calculator page opens on the US Army method and compares the estimate with the Army maximum for your age group and sex.
Privacy
Nothing is uploaded: every calculation runs in your browser and your measurements never leave your device.
Related tools
Check your body mass index with the BMI Calculator, estimate lean mass with three formulas in the Lean Body Mass Calculator, or convert between kilograms and pounds with the Mass Converter and between centimetres and inches with the Length Converter.
Sources
- Hodgdon J.A., Beckett M.B. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center reports 84-11 and 84-29, San Diego, 1984.
- US Department of Defense. DoD Instruction 1308.3, DoD Physical Fitness and Body Fat Programs Procedures.
- Deurenberg P., Weststrate J.A., Seidell J.C. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition 1991; 65: 105–114.
- American Council on Exercise. Percent body fat norms.
- US Army. Army Directive 2023-11, Army Body Fat Assessment for the Army Body Composition Program, 2023.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party library. They follow the published formulas listed above: the US Navy circumference equations of Hodgdon and Beckett, the Deurenberg BMI equation, the US Army 2023 one-site tape equation and the ACE category bands.
Frequently asked questions
How accurate is the US Navy body fat method?
In the original studies by Hodgdon and Beckett, the Navy equations predicted body fat within about 3 to 4 percentage points of underwater weighing for most people. Careful, repeated tape measurements matter more than anything else: a waist reading that is 2 cm too large can move the result by more than a percentage point.
Why does the BMI method give a different answer?
The BMI method of Deurenberg and colleagues uses only weight, height, age and sex, so it cannot tell muscle from fat. It tends to overestimate body fat in muscular people and underestimate it in people with little muscle. The tape method looks at where the body carries its size, so it usually tracks individual body fat more closely.
Why do metric and US units give slightly different Navy results?
The Navy method was published in two forms: an inch form used by the US Department of Defense and a centimetre form written through body density and the Siri equation. They are fits of the same data rather than exact unit conversions of each other, so they can differ by a fraction of a percentage point. The calculator uses the form that matches the units you choose.
What do the ACE categories mean?
The American Council on Exercise groups body fat into essential fat, athletes, fitness, average and obese. Essential fat is the minimum needed for normal body function, about 2 to 5 % for men and 10 to 13 % for women. The bands are a general guide for adults and do not account for age.
What is the difference between fat mass and lean mass?
Fat mass is the weight of body fat: your weight multiplied by the body fat percentage. Lean mass is everything else, including muscle, bone, organs and water. For example, 25 % body fat at 80 kg is 20 kg of fat mass and 60 kg of lean mass.