Body fat percentage calculator

The two methods

The US Navy method (Hodgdon and Beckett, 1984) was designed to screen recruits with only a tape measure. It uses base-10 logarithms and measurements in centimeters; the calculator converts inches for you.

\[ \begin{gathered} \text{Men} \ :\ \dfrac{495}{1.0324 - 0.19077 \times \log(\text{waist} - \text{neck}) + 0.15456 \times \log(\text{height})} - 450 \\ \text{Women} \ :\ \dfrac{495}{1.29579 - 0.35004 \times \log(\text{waist} + \text{hip} - \text{neck}) + 0.22100 \times \log(\text{height})} - 450 \\ \text{Deurenberg} \ :\ 1.20 \times \text{BMI} + 0.23 \times \text{age} - 10.8 \times \text{sex} - 5.4 \quad (\text{sex} = 1 \, \text{for men} ,\ 0 \, \text{for women}) \end{gathered} \]

The Deurenberg formula (1991) needs only BMI, age and sex. It is less accurate because it ignores your actual build; the Navy method is better if you measure carefully.

Body fat categories

These ranges come from the American Council on Exercise. Women naturally carry more essential fat than men because of hormonal and reproductive functions.

How to measure correctly

• Measure in the morning, before eating, with the tape flat and snug but not squeezing.
• Neck: just below the larynx, tape level.
• Waist: at the navel for men, at the narrowest part of the torso for women.
• Hips (women): at the widest point.
• Take each measurement three times and average them, and repeat them the same way each time you track progress.

Body fat calculator: measure correctly with a tape

The body fat calculator is only as good as your measurements. First, measure in the morning, before eating, in no tight clothing. Then wrap the tape without pressing into the skin. Next, measure the neck below the Adam's apple, the waist at the navel and, for women, the hips at the widest point. Finally, repeat each measurement twice and use the average.

For example, a 0.5 inch error at the waist shifts the result by about 1 point. So always measure at the same spot. In fact, the trend from month to month matters more than a single number.

Body fat calculator: reference categories

The ranges below are common guides. However, they vary by age and source.

Women carry more essential fat than men, because they need it for hormone function. Therefore, never compare the two columns.

Body fat calculator: pair it with BMI and ideal weight

Body fat complements BMI well. For example, two people can share a BMI yet differ in makeup. So read the BMI calculator and body fat together. Then the ideal weight calculator gives a weight target, while body fat shows the quality of that weight.

Finally, to match your eating to a goal, use the calorie calculator. This result is an estimate and does not replace medical advice.

Body fat calculator: track your progress

To track body fat, measure yourself every two to four weeks. First, pick a fixed moment, such as Sunday morning. Then always use the same tape. Next, write the three values in a notebook. That way, you see the trend instead of reacting to one number.

For example, going from 22% to 20% in three months is a good pace. However, a drop of 6 points in one month should raise a flag, because it often comes from a measuring error. Also, gaining muscle can keep your weight steady while body fat falls. Finally, keep a starting photo to compare.