How to use the body fat calculator
- Choose the sex whose formula you want and US or metric units, then enter your height.
- Measure your neck just below the larynx, your waist (at the navel for males, at the narrowest point for females) and, for the female formula, your hips at the widest point. Keep the tape snug but not tight, and stand relaxed.
- Optionally enter your weight to see estimated fat mass and lean mass.
- Read the body fat percentage. Repeat the measurements a few times and average them, because small tape differences change the result.
Formula
Male: body fat % = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76
Female: body fat % = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387
All lengths in inches. Centimeters are divided by 2.54 first.
Fat mass = weight x body fat %, lean mass = weight - fat mass
This is the inch form of the US Navy circumference method by Hodgdon and Beckett. A separate centimeter form with different coefficients is also published, and the two agree within about a third of a percentage point in the checks made for this page.
Worked example
A male who is 70 in tall with a 15 in neck and a 34 in waist has waist minus neck of 19. The formula gives 86.010 x log10(19) - 70.041 x log10(70) + 36.76 = 17.5 percent.
For a 200 lb person that is about 35.0 lb of fat and 165.0 lb of lean mass.
A female who is 65 in tall with a 15 in neck, a 30 in waist and a 38 in hip has waist plus hip minus neck of 53. The formula gives 163.205 x log10(53) - 97.684 x log10(65) - 78.387 = 25.9 percent.
The separately published centimeter form gives 17.4 and 25.7 for the same two people, close to the inch-form results.
How the Navy method works
The method estimates body density from circumferences and height, and then converts density to a body fat percentage. Neck size acts as a proxy for lean upper-body mass, while waist and hip size reflect fat stored around the middle. Because it needs only a tape measure, it is easy to repeat at home, which is its main advantage.
Known limits
A tape measure estimate is not a medical measurement.
- Individual errors of several percentage points are common compared with lab methods such as DEXA.
- Tape position matters: a waist measured an inch higher or lower changes the result noticeably.
- The formulas were developed on military personnel, so they may fit other groups less well.
- Bloating, hydration and time of day move your waist measurement.
- Results outside about 2 to 60 percent are rejected because the formula cannot describe them.
Using the number
The most useful thing to do with a tape-based estimate is to track change over weeks under the same conditions, not to compare it with someone else's number. If body composition matters for a health decision, ask a clinician about better measurements. For related checks, see the BMI calculator and the TDEE calculator.
Assumptions and limits
- Adults only. The equations were not built for children, teens, pregnancy or people with edema.
- Only two sex-specific equation sets exist for this method, so you choose the set that matches the data the equation was fitted on.
- Height must be between 4 ft and 8 ft (122 to 244 cm), and measurements must be plausible for an adult.
- No category labels such as "athlete" or "obese" are given, because published category tables differ and this tool avoids implying a diagnosis.
- Estimates are for general information. They are not medical advice. Nothing you enter leaves your browser.
Frequently asked questions
How accurate is the US Navy body fat calculation?
It is a rough estimate. Compared with laboratory methods it can be off by several percentage points for an individual, mostly because of how the tape is placed and how well the formula fits your body type.
Where do I measure my waist for the Navy method?
For the male formula, measure at the navel. For the female formula, measure at the narrowest point of the waist. Keep the tape level and snug without compressing the skin, and measure after a normal exhale.
Why do I need hip measurements as a female?
The female equation includes the hip circumference, which reflects fat stored in the lower body. The male equation does not use it, so the hip field is ignored for males.
Why was my result rejected?
The formula needs the waist to be larger than the neck (and waist plus hip larger than neck for the female formula), and it only describes body fat between about 2 and 60 percent. If your measurements fall outside that, recheck the tape placement and units.
Is a lower body fat percentage always better?
No. Some body fat is essential for normal function, and the right level depends on age, sex, health and goals. This tool gives an estimate, not a target. A clinician can help you set one.