Body Fat Calculator
This body fat calculator estimates body fat percentage from a few tape-measure readings, using the circumference equations developed for the U.S. Navy. Add your weight to see fat mass and lean mass as well.
Result
17.5% body fat
| Body fat (U.S. Navy method) | 17.5% |
|---|---|
| Fat mass | 31 lb |
| Lean mass | 144 lb |
An estimate from tape measurements. Measure carefully, at the same points each time, to track changes.
How the Navy Body Fat Method Works
Measuring body fat directly takes laboratory equipment. In 1984, researchers at the Naval Health Research Center developed equations that estimate it from a tape measure instead. They measured body composition in the lab, then found how well neck, waist, hip and height measurements predicted it. The resulting equations are still widely used because they need nothing more than a tape.
The Equations
All measurements are in inches. The calculator converts metric inputs first.
Men: % body fat = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76
Women: % body fat = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
“log₁₀” is the base-10 logarithm (the “log” key on most calculators).
Fat mass and lean mass
If you enter your weight:
- Fat mass = weight × body fat % ÷ 100
- Lean mass = weight − fat mass
Worked Example
A man 5 ft 10 in (70 in) tall, with a 15 in neck and a 34 in abdomen, weighing 175 lb:
- Abdomen − neck: 34 − 15 = 19
- 86.010 × log₁₀(19) = 86.010 × 1.2788 = 109.99
- 70.041 × log₁₀(70) = 70.041 × 1.8451 = 129.23
- Body fat: 109.99 − 129.23 + 36.76 = 17.5%
- Fat mass: 175 × 0.175 = 30.6 lb
- Lean mass: 175 − 30.6 = 144.4 lb
For a woman 5 ft 5 in (65 in) with a 13 in neck, 28 in waist and 38 in hips: waist + hip − neck = 53, and 163.205 × log₁₀(53) − 97.684 × log₁₀(65) − 78.387 = 25.9%.
How to Measure
| Measurement | Where |
|---|---|
| Height | Standing straight, without shoes |
| Neck | Just below the larynx (Adam’s apple), tape sloping slightly down to the front |
| Abdomen (men) | Around the navel, relaxed, at the end of a normal breath out |
| Waist (women) | At the narrowest point of the torso |
| Hips (women) | At the widest point of the buttocks |
Keep the tape level and snug against the skin without pressing in. Take each measurement two or three times and use the average.
Tips and Limitations
Consistency beats precision
Small measuring differences change the result. If you’re tracking changes over time, measure at the same spots, at the same time of day, with the same tape, ideally with someone else holding it.
It’s an estimate from body shape
The equations predict fat from circumferences, so people whose shape differs from the original study groups may get less accurate results. The Naval Health Research Center has itself noted that service members questioned the equations’ accuracy.
Compare with other measures
Body fat percentage and BMI answer different questions. Looking at both, along with waist size, gives a fuller picture than any single number. For questions about what a result means for your own health, talk to a doctor.
To see a weight range rather than a percentage, use the ideal weight calculator.
Frequently Asked Questions
How does the Navy body fat method work?
It estimates body fat from circumference measurements and height. Men use neck and abdomen; women use neck, waist and hips. The equations were developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 from people whose body composition was measured in the lab.
Where do I measure my neck, waist and hips?
Measure the neck just below the larynx (Adam's apple). Men measure the abdomen around the navel; women measure the natural waist at its narrowest point and the hips at the widest point of the buttocks. Keep the tape level and snug without compressing the skin.
Do I need my weight?
No. The body fat percentage comes from height and circumferences only. Weight is optional and lets the calculator split total weight into fat mass and lean mass.
How accurate is a tape-measure body fat estimate?
It's an estimate. The equations predict body fat from body shape, so results depend on careful, consistent measuring and can differ from lab methods. A Naval Health Research Center report notes that many sailors question the accuracy of the equations.
Why do men and women use different measurements?
The original research developed separate equations for men and women, because fat is typically distributed differently. The women's equation adds a hip measurement, and the coefficients differ.
Is body fat percentage better than BMI?
They measure different things. BMI compares weight with height and can't separate fat from muscle. A body fat estimate looks at composition. Both are screening tools rather than diagnoses.
Related Calculators
- BMI CalculatorBody mass index, CDC weight category and healthy weight range.
- Ideal Weight CalculatorHealthy weight range for your height, plus four classic formulas.
- Calorie CalculatorDaily calories to maintain weight, at four activity levels.
- BMR CalculatorCalories burned at rest, using the Mifflin–St Jeor equation.
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, 1984 (DTIC ADA143890)
- Hodgdon and Beckett, Naval Health Research Center, 1984 (DTIC ADA146456)
- Naval Health Research Center report noting that many sailors question the accuracy of the Navy body fat equations (DTIC ADA370117)
- Equation coefficients as published by Topend Sports, citing Hodgdon and Beckett (1984); all measurements in inches.
- Metric inputs are converted to inches before the equations are applied.
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