This body fat calculator compares the BMI method with the Navy circumference method. Both give approximate estimates, rather than a direct measurement of body fat.
Enter age (18 or older), sex, height and circumferences
In older age, muscle mass and general condition matter when interpreting BMI. Winter et al. (2014) describe limitations of the usual BMI interpretation in older adults. Winter et al., 2014. BMI by age
Adult reference ranges
Below the reference rangeunder 18.5Current range
Within the reference range18.5 to 24.9Current range
Above the reference range25 to 29.9Current range
Well above the reference range30 or moreCurrent range
This estimate is approximate. The BMI method has uncertainty of about ±4 percentage points (Deurenberg 1991). Deurenberg, 1991.
This calculator gives general reference values and does not replace advice from a doctor. For children and teens under 18, during pregnancy and breastfeeding, for very muscular builds and in older age, the results are of limited use.
How this calculator works
The US Navy method (Hodgdon and Beckett, 1984) uses your height plus your waist and neck, and for women also your hip. For comparison it shows an estimate from BMI (Deurenberg, 1991), which also takes age and sex into account. Both are estimates. The BMI method has uncertainty of about ±4 percentage points.
Measure at the same spot each time so your readings stay comparable. For the Navy method, men measure the waist at the navel and women at the narrowest point. The WHO waist protocol instead uses the midpoint between the lowest rib and the top of the hip bone. These measurement sites are not interchangeable.
What each one measures
BMI relates weight to height. It does not know what the weight is made of. Body fat percentage describes how much of your weight is fat. Two people with the same BMI can have very different percentages. A formula can only estimate this share, not measure it directly.
This calculator gives general reference values and does not replace advice from a doctor. For children and teens under 18, during pregnancy and breastfeeding, for very muscular builds and in older age, the results are of limited use.