How to use the body fat calculator
- Choose Male or Female, then US (in, lb) or Metric (cm, kg).
- Enter Height and Weight. Weight is optional: leave it empty to see the percentage without fat and lean mass.
- Measure your Waist and Neck, plus your Hip if you chose Female. The hint under the fields shows where the tape goes for your sex.
- Read the percentage, category, fat mass, and lean mass. The result updates as you type.
How the Navy method works
The equations come from Hodgdon and Beckett (1984, Naval Health Research Center) and appear in DoD Instruction 1308.3. The DoD report on developing the equations explains them. All lengths are in inches, and metric entries are converted first:
- Men: body fat % = 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76
- Women: body fat % = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387
Categories use the American Council on Exercise (ACE) ranges, chosen after the percentage is rounded to one decimal:
- Men: essential fat 2% to 5%, athletes 6% to 13%, fitness 14% to 17%, acceptable 18% to 24%, obese 25% and above
- Women: essential fat 10% to 13%, athletes 14% to 20%, fitness 21% to 24%, acceptable 25% to 31%, obese 32% and above
Worked example
The starting inputs are a man who is 5 ft 10 in (70 in) and 175 lb, with a 34 in waist and a 15 in neck. Waist minus neck is 19 in, so body fat = 86.010 × log10(19) - 70.041 × log10(70) + 36.76 = 109.99 - 129.23 + 36.76 = 17.5%, in the Fitness range. Fat mass is 175 × 0.175 = 30.6 lb and lean mass is 144.4 lb.
Limits and edge cases
This is a tape-measure estimate, not a medical test. In the example, half an inch of waist error shifts the result by about one percentage point, so measure three times and average. Hydration and posture also matter, and the method is less reliable for older adults, very lean athletes, and people with very high body fat.
A man's waist must be larger than his neck, and each measurement must be realistic, or an error appears next to the field. A formula result of zero or less, or 75% or more, asks you to re-check your readings. Related tools: lean body mass calculator, waist-to-hip ratio calculator, BMI calculator, and the macro calculator for protein targets.
Frequently asked questions
How accurate is the Navy body fat calculator?
It is an estimate that can be off by several percentage points compared with a DEXA scan, and tape errors add to that: half an inch of waist error moves a man's result by about 1 point. It works best for tracking your own trend when you measure the same way each time.
Where do I measure my waist for the Navy method?
Men measure across the navel (belly button). Women measure at the narrowest part of the natural waist, about halfway between the navel and the bottom of the breastbone. Measure after a normal breath out, with the tape level and snug but not tight.
Why do women need a hip measurement?
The Navy method uses separate equations for men and women. The women's equation adds hip circumference, which captures how fat is distributed on the body. The men's equation uses only height, neck, and waist.
What is a healthy body fat percentage?
By the American Council on Exercise chart, the fitness range is 14% to 17% for men and 21% to 24% for women, and the acceptable range is 18% to 24% for men and 25% to 31% for women. Essential fat, the minimum the body needs, is 2% to 5% for men and 10% to 13% for women.
Does this work for very muscular people?
Not always. A thick, muscular neck lowers the estimate, while a thick, muscular trunk raises it, so results can be off in either direction. A DEXA scan or skinfold test is a better check.
Sources: DoD body composition equations (DTIC); Hodgdon and Beckett, Naval Health Research Center reports 84-11 and 84-29 (1984); ACE body fat guidelines. Not medical advice.