How accurate is the Navy circumference method?

For most people it lands within a few percentage points of lab methods, which is enough to track direction. The bigger source of error is inconsistent measuring — same tape, same spots, same time of day matters more than the formula.

Where exactly do I measure?

Neck: just below the larynx, tape sloping slightly down at the front. Waist: men at the navel, women at the narrowest point. Hips (women): at the widest point. Tape snug against the skin but not compressing it.

Why does my smart scale say something different?

Scales estimate body fat by passing a small current through you, and that reading swings with hydration, food and time of day. Neither method is a lab measurement. Pick one, use it consistently, and track the trend rather than the single number.

What do fat mass and lean mass tell me?

They split your weight into the part you're usually trying to reduce and the part you're trying to keep. Watching lean mass across a cut tells you whether the weight you're losing is the weight you meant to lose.

Body composition calculator

The scale tells you what you weigh, not what you’re made of. This calculator estimates body fat percentage — and from it, fat mass and lean mass — using the US Navy circumference method: nothing but a tape measure and three or four measurements.

Measure carefully, enter your numbers, and read the result below. Consistency between measurements matters more than any single reading.

AION

I can estimate your body fat from tape measurements — the US Navy method. Grab a tape measure; I need four or five numbers, measured relaxed, not sucked in.

AION

First — pounds and inches, or kilos and centimeters?

Common questions

How accurate is the Navy circumference method?: For most people it lands within a few percentage points of lab methods, which is enough to track direction. The bigger source of error is inconsistent measuring — same tape, same spots, same time of day matters more than the formula.
Where exactly do I measure?: Neck: just below the larynx, tape sloping slightly down at the front. Waist: men at the navel, women at the narrowest point. Hips (women): at the widest point. Tape snug against the skin but not compressing it.
Why does my smart scale say something different?: Scales estimate body fat by passing a small current through you, and that reading swings with hydration, food and time of day. Neither method is a lab measurement. Pick one, use it consistently, and track the trend rather than the single number.
What do fat mass and lean mass tell me?: They split your weight into the part you're usually trying to reduce and the part you're trying to keep. Watching lean mass across a cut tells you whether the weight you're losing is the weight you meant to lose.