Key facts
- Calculated as weight (kg) divided by height (m) squared.
- A quick population-level screening tool.
- Doesn't distinguish muscle from fat.
- Often misclassifies muscular individuals.
BMI is a quick calculation — your weight in kilograms divided by your height in metres squared — that sorts people into weight categories. It's useful as a population-level screening tool because it's fast and requires no equipment.
Its big limitation is that it only knows your weight and height, not what that weight is made of. A muscular athlete and an out-of-shape person can have the same BMI, and lifters are frequently labeled 'overweight' despite low body fat. For individuals focused on fitness, body fat percentage and FFMI are far more informative.
Frequently asked questions
Is BMI accurate for athletes?
Often not. BMI can't tell muscle from fat, so muscular people are frequently misclassified as overweight. Body fat percentage or FFMI is more useful for them.
What is a normal BMI?
A BMI of 18.5–24.9 is generally classed as 'normal weight', but this is a population guideline and doesn't account for body composition.
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