BMI vs Body Fat Percentage
What's the difference between BMI and body fat percentage? Compare what each one measures, accuracy, and when to use each.
Reviewed Jan 15, 2025
Quick answer
BMI is a weight-to-height ratio that says nothing about composition. Body fat percentage measures how much of your weight is actually fat. BMI is a fast screen; body fat is the more direct number.
What BMI measures
BMI = weight (kg) ÷ height (m)². It's a single number that compares you to a standard healthy range, but it can't tell muscle from fat.
What body fat percentage measures
Body fat percentage estimates the share of your body weight that's fat tissue. It separates lean mass (muscle, bone, water, organs) from fat — which is what most people actually care about.
When to use each
- Use BMI for a fast, reproducible screening number — especially in clinical settings.
- Use body fat percentage if you're muscular, training seriously, or want a more nuanced picture.
- Track both over time rather than chasing a single reading.