Body Composition Calculator

The Navy method directly measures circumferences that correlate with fat distribution in specific body regions, then uses a logarithmic formula validated against hydrostatic (underwater) weighing. The BMI-based regression uses only weight, height, and age - inputs that cannot separate fat from muscle - so it has substantially higher error, especially in athletic or elderly individuals.

Lean mass (also called fat-free mass) includes muscle, bone, organs, water, and connective tissue - everything that is not fat. Higher lean mass raises your resting metabolic rate, supports strength and mobility, protects against injury, and is associated with better long-term health outcomes independent of BMI or body fat percentage.

Yes, and trends matter more than single readings. Measure under the same conditions (morning, fasted, same time of cycle for women) and use the same method each time. A consistent decrease in body fat percentage alongside stable or rising lean mass is a positive sign regardless of what the scale shows.

Percentages below essential fat (under about 3-5% for men) are dangerous and associated with organ stress, hormonal disruption, and immune suppression. The 13% threshold labeled 'Essential Fat' in the calculator is the lower end where body function is still maintained, but values below 6-8% are typically only seen in competitive athletes during peak conditioning and are not sustainable long-term. This calculator is for informational purposes only and does not constitute medical advice.