Body Fat Calculator (US Navy Method)

The US Navy body fat method estimates body fat percentage using simple tape-measure circumferences. It eliminates the need for underwater weighing or DEXA scans (a clinical-grade body composition scan). It’s accurate to within about ±3-4% of laboratory methods, which is good enough for tracking progress.

The Formulas (Inches)

The original formulas use inches, so this calculator converts metric inputs to inches internally before applying them.

Men:

% Body Fat = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76

Women:

% Body Fat = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

How to Measure

The accuracy depends entirely on getting the measurements right.

• Neck. Just below the larynx (Adam’s apple), perpendicular to the neck’s long axis. Don’t pull tight.
• Abdomen (men). At navel level, horizontal, after a normal exhale. Don’t suck in.
• Waist (women). At the narrowest point of the torso, horizontal.
• Hip (women). At the widest point of the buttocks, horizontal.
• Height. Without shoes.

A flexible cloth or fiberglass tape gives the cleanest reading. Avoid stretchy fabric tapes. Repeat each measurement twice and average if they differ.

Body Fat Reference Ranges

Women carry more essential fat for biological reasons (reproductive function), which is why the women’s “athletic” range starts higher than the men’s.

What the Calculator Returns

• Body fat percentage. Your estimate, plus the range a lab method would probably land in.
• Fat mass. Weight × body fat %, the kilograms or pounds that are fat tissue.
• Lean mass. Weight minus fat mass: muscle, bone, organs, water.
• Category. Where you fall on the reference ranges above.
• Distance to the next category, in kilograms or pounds of fat, holding lean mass fixed.

Worked Example

Male, 70 inches (5'10"), neck 15 inches, abdomen 36 inches:

% Body Fat = 86.010 × log₁₀(36 − 15) − 70.041 × log₁₀(70) + 36.76 = 86.010 × log₁₀(21) − 70.041 × 1.84510 + 36.76 = 86.010 × 1.32222 − 129.233 + 36.76 = 113.734 − 129.233 + 36.76 = 21.3% body fat, the Average range

The metric equivalent is close but not identical. 178 cm, 38 cm neck and 91 cm abdomen convert to 70.08, 14.96 and 35.83 inches, which gives 21.0%. That third of a point is not the formula disagreeing with itself, it is the rounding you did when you wrote down whole centimeters for measurements that were never whole inches. It is also a fair guide to how much precision this method really has.

Limitations

The Navy method assumes “normal” body proportions. Outliers it doesn’t handle well:

• Bodybuilders with thick necks may score artificially low
• People with significant abdominal muscle hypertrophy (large rectus abdominis) may score higher than reality
• Pregnant women. The formula isn’t valid. Use pre-pregnancy values.
• Very short or very tall people. Accuracy drops at the extremes.

For tracking progress, what matters most is consistency. Use the same tape, same measurement spots, same time of day. The week-over-week change is more reliable than the absolute number.