About the Body Fat Calculator
This body fat calculator estimates what share of your weight is fat, using the US Navy circumference method — the Hodgdon–Beckett tape-measure equations that the US Department of Defense used for decades in military body composition checks. Men need height, neck and waist measurements; women also add the hips. You can switch to a BMI-based estimate (the Deurenberg equation) if you do not have a tape measure handy.
Besides the percentage, you get your fat mass and lean mass in pounds or kilograms and the American Council on Exercise (ACE) category the result falls in, from essential fat through athletic, fitness and average to obese. Tracking body fat over time is more informative than weight alone when you are building muscle or dieting.
Tape methods usually land within about 3–4 percentage points of lab methods such as DEXA or underwater weighing when measurements are taken carefully. Measure on bare skin, keep the tape level and snug but not compressing, and take the average of three readings.
With the default inputs, the body fat is 16.5%. Change any value above to recalculate instantly.
How to use the body fat calculator
- 1Choose the Navy tape method, or the BMI estimate if you have no tape measure.
- 2Select your sex, enter your age and choose US or metric units.
- 3Enter height and weight.
- 4Measure your neck and waist (and hips for women) and enter the values.
- 5Read your body fat percentage, category and fat vs lean mass.
Formula and method
The US Navy equations (Hodgdon and Beckett) estimate body density from circumferences and height, all measured in inches; metric measurements are converted to inches first so the published coefficients apply. The waist-minus-neck girth captures abdominal fat while correcting for frame size, and women add hip circumference because they store more fat there.
The BMI-based Deurenberg equation estimates body fat from BMI, age and sex (sex = 1 for men, 0 for women). It needs no tape, but it inherits BMI’s blind spot for muscle, so it overestimates fat in muscular people. Fat mass is weight × body fat %, and lean mass is the rest. Results are clamped to 2–65% to avoid impossible values from mistyped measurements.
- waist, neck, hip
- Circumferences in inches
- height
- Height in inches
- BMI
- Body mass index, kg/m²
- sex
- 1 for men, 0 for women (Deurenberg only)
Worked examples
Man, 5 ft 10 in, 180 lb, neck 15.5 in, waist 34 in
Waist minus neck is 18.5 inches. 86.010 × log10(18.5) − 70.041 × log10(70) + 36.76 ≈ 16.5%, which falls in the ACE fitness range for men. At 180 lb that is about 29.7 lb of fat and 150.3 lb of lean mass.
Woman, 165 cm, 65 kg, neck 33 cm, waist 74 cm, hips 100 cm
Converted to inches, waist + hip − neck is 55.5 in and height is 64.96 in. The women’s Navy equation gives about 29.2% body fat — the ACE average range — or roughly 19.0 kg of fat mass.
BMI-based estimate: 40-year-old man, 6 ft, 200 lb
At 72 inches and 200 lb his BMI is about 27.1. Deurenberg: 1.20 × 27.1 + 0.23 × 40 − 10.8 − 5.4 ≈ 25.5% body fat, just into the ACE obese range for men. The Navy tape method would give a different, usually more precise, figure for a muscular person.
Frequently asked questions
How accurate is the US Navy body fat method?+
With careful measurements it typically agrees with lab methods such as DEXA or hydrostatic weighing to within about 3–4 percentage points for most people. Errors grow for very lean or very heavy individuals and when the tape is placed inconsistently.
What is a healthy body fat percentage?+
The American Council on Exercise puts average body fat at 18–24% for men and 25–31% for women, with fitness levels at 14–17% and 21–24%. Essential fat, needed for normal function, is about 2–5% in men and 10–13% in women.
Where exactly should I measure my waist?+
For the Navy formula men measure the waist horizontally at the navel, and women at the narrowest point of the abdomen. Measure after breathing out normally, without pulling in your stomach.
Why is my body fat estimate different from my smart scale?+
Smart scales use bioelectrical impedance, which is sensitive to hydration, meals and exercise, and can vary by several percent from day to day. Tape methods and scales use different assumptions, so track the trend from one method consistently rather than comparing them.
Is body fat percentage better than BMI?+
It is more informative because it separates fat from muscle. Two people with the same BMI can have very different body fat levels. BMI is still useful as a quick screen because it only needs height and weight.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.