How to Calculate Your Body Fat Percentage

Body fat percentage gives a more complete picture than weight or BMI alone, since it separates fat mass from everything else (muscle, bone, water). The most accessible method that doesn't require special equipment is the US Navy circumference method — here's how to do it properly.

Step 1: Take the right measurements

You'll need neck circumference (measured just below the larynx, tape sloping slightly downward at the front), waist circumference (at the narrowest point, usually just above the belly button), and for women, hip circumference (at the widest point) as well. Height is also required.

Step 2: Measure carefully, not just quickly

Measure at the same time of day for consistency (mornings, before eating, tend to be most stable), without pulling the tape tight enough to compress skin, and standing in a relaxed, natural posture. Inconsistent technique between measurements is the most common source of misleading "changes" that aren't real.

Step 3: Apply the formula (or skip to the calculator)

Men: BF% = 495 / (1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450
Women: BF% = 495 / (1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.221×log₁₀(height)) − 450

The Body Fat Calculator handles this calculation directly from your measurements, so you don't need to work through the logarithms by hand.

How accurate is this, really?

Validation studies comparing this method against underwater weighing typically find it accurate to within about 3-4% body fat for most adults — good enough to track meaningful trends over weeks and months, even though it's an estimate rather than a lab-grade measurement.

Track the trend, not any single reading

Like most body composition measurements, a single reading carries some noise. Measuring consistently every few weeks and watching the trend line tells a far more reliable story than treating any one measurement as definitive.