Body-fat estimates explained

Body-fat percentage is the fraction of your mass that is fat tissue versus lean mass (muscle, bone, water, organs). Clinical gold standards — DEXA, hydrostatic weighing, MRI — need equipment most people lack. Field methods use calipers or a tape measure with published regression equations. Our Body Fat Estimate calculator implements the U.S. Navy circumference method.

Navy method inputs

Men: height, neck, and waist (abdomen at navel level). Women: height, neck, waist, and hip (widest gluteal circumference). Measurements are taken in centimetres or inches with consistent tension on the tape — not pulled tight, not sagging.

What the formula does

The Navy equations combine circumferences into a density estimate, then apply a body-fat conversion (Siri or similar). Log terms penalise larger waist relative to neck and height. Results are rounded for display but remain estimates with several percentage points of typical error versus DEXA.

Worked example (illustrative)

A man 180 cm tall with 40 cm neck and 90 cm waist might land near the high teens to low twenties percent depending on exact measurement technique — run your numbers in the tool rather than extrapolating from this sentence alone.

Strengths and limits

• Pros — cheap, repeatable at home, tracks trend if you measure the same way each time.
• Cons — sensitive to bloating, posture, and where exactly you place the tape; less accurate for very lean or very high body-fat extremes.

Pair with waist-to-height ratio (Waist-to-Height Ratio Tool) and BMI (Body Indexes) for broader context — not diagnosis.

FAQs

How often should I measure?

Monthly is enough for trends; daily noise from water dominates.

Why hip for women only?

The female Navy equation includes gluteal hip to model fat distribution differences.

Can I compare to gym scale bioimpedance?

Trends may align; absolute numbers often disagree between methods.

Sources

U.S. Navy body composition assessment procedures; Hodgdon & Beckett circumference equations.