Body Fat Percentage Calculator

The US Navy Method

This calculator uses the US Navy circumference method to estimate body fat percentage from height and tape measurements. The estimate is not a direct measurement and may not fit every body type.

The Formulas

For Men:

$$\text{Body Fat \%} = 86.010 \times \log_{10}(\text{waist} - \text{neck}) - 70.041 \times \log_{10}(\text{height}) + 36.76$$

For Women:

$$\text{Body Fat \%} = 163.205 \times \log_{10}(\text{waist} + \text{hip} - \text{neck}) - 97.684 \times \log_{10}(\text{height}) - 78.387$$

Where all measurements are in centimeters.

Why These Measurements?

The equations use the combined measurements as inputs; they do not directly measure fat or assess health risk.

Measurement Protocol

For more consistent measurements:

Neck

• Measure below the larynx (Adam's apple)
• Tape perpendicular to the long axis of the neck
• Shoulders relaxed, head looking straight forward

Waist

• All users: At the navel (umbilicus) level
• Stand relaxed, don't suck in

Hips (Women Only)

• At the widest point of the buttocks/hip region
• Feet together, weight evenly distributed

General Tips

• Use a non-stretch tape measure (metal or fiberglass)
• Keep tape snug but not compressing skin
• Take 3 measurements, use the average
• Measure same time daily (morning preferred)
• Don't measure after exercise, large meals, or dehydration

Body Composition Calculations

When you provide weight, we calculate:

$$\text{Fat Mass (kg)} = \frac{\text{Body Fat \%}}{100} \times \text{Total Weight (kg)}$$

$$\text{Lean Mass (kg)} = \text{Total Weight (kg)} - \text{Fat Mass (kg)}$$

General Reference Range

Weight Comparison

When weight is provided, the calculator compares it with the midpoint of the range above while assuming lean mass stays constant. This is a mathematical comparison, not a personalized target or recommendation to change weight.

$$\text{Estimated Weight at Reference Body Fat} = \frac{\text{Lean Mass}}{1 - (\text{Reference Body Fat \%}/100)}$$

Accuracy and Limitations

• Tape placement and tension affect the result. Take measurements consistently if you are tracking changes.
• The formula may be less representative for very muscular people or people whose body shape differs from the populations it was developed for.
• The broad comparison categories do not account for age and are not a diagnosis or personal health target.
• This calculator is not designed for children or pregnancy.