Body Fat Calculator

How It Works

This calculator uses a circumference-based formula that estimates body fat percentage from body measurements. It converts metric entries to inches when needed, then applies a Navy-style logarithmic equation. The estimated body fat percentage is combined with body weight to estimate fat mass and lean mass.

Example

A 69-inch male with a 15.5-inch neck, 33.5-inch waist, and body weight of 165 lb estimates around 15.9% body fat. That works out to roughly 26.3 lb of fat mass and 138.7 lb of estimated lean mass.

When to use this calculator

• Use it when scale weight alone is not giving enough context about body composition change.
• Use it when you want a quick home estimate before checking more advanced measurement options.
• Use it when comparing nutrition or training phases, while keeping the method consistent each time.

How to measure more consistently

• Measure the neck and waist with the tape level against the skin or over thin clothing.
• Do not pull the tape so tight that it compresses soft tissue.
• For women using this method, measure the hips around the largest glute area.
• Repeat measurements if needed and use steady technique when tracking progress over time.

How to interpret the estimate

• Body fat percentage is different from body weight or BMI because it focuses on body composition.
• The fat-mass and lean-mass outputs are derived from the estimated percentage, not from direct scanning.
• Use the result for rough progress tracking, not as a single health verdict.

Important limitations

• Circumference formulas can be sensitive to small measurement errors.
• Different formulas and devices can produce different numbers.
• Age, training background, body type, and medical context all matter when interpreting the result.