Body composition · FitScan

How to Calculate Your Body Fat Percentage (Without a DEXA Scan)

Your bathroom scale can't tell the difference between a pound of fat and a pound of muscle, but your body fat percentage can. It's the single most useful number for understanding how your body is actually changing. Here's how to estimate it accurately without an expensive lab scan.

Why body fat percentage beats the scale

Two people can weigh exactly the same and look completely different. Weight lumps together fat, muscle, water and bone into one meaningless number. Body fat percentage separates the part you usually want to lose (fat) from the part you want to keep or build (lean mass). When you diet, the scale dropping could mean you lost fat, or muscle and water. Tracking body fat percentage tells you which, so you can adjust before you lose the muscle that keeps your metabolism high.

The U.S. Navy circumference method

The most reliable at-home method uses a tape measure, not a photo or a guess. The U.S. Navy formula estimates body fat from your height plus a few circumferences: neck and waist for men, and neck, waist and hips for women. It's accurate to within a few percentage points for most people, costs nothing, and only needs a soft tape measure. Measure first thing in the morning, relaxed, without sucking in, and take each measurement twice. Consistency matters more than perfection, measuring the same way every time means your trend is trustworthy even if the absolute number is a point or two off.

BMI-based estimates

If you don't have a tape measure, a BMI-based estimate (the Deurenberg equation) gives a rough body fat percentage from your height, weight, age and sex. It's less accurate than the Navy method, it can't tell a muscular person from an out-of-shape one at the same weight, but it's a reasonable starting baseline that improves the moment you add measurements.

Add progress photos for the full picture

Numbers lie a little; photos don't. Front and side photos taken in the same lighting and pose every week or two reveal changes that any single measurement misses. Pair photos with your body fat estimate and your weight, and you have a three-way cross-check: when the photo, the tape and the trend all agree, you know exactly what's happening.

How FitScan does it for you

FitScan combines all three. Enter your weight and a couple of measurements, snap a front and side photo, and it computes your body fat percentage using the Navy method when measurements are available and a BMI-based estimate when they're not, then stores your photos locally so you can line them up side by side over time. Your first body scan is free.

Related feature: Body Scan & Composition Report →