BMI Calculator
Body mass index from your height and weight, in either metric or imperial units, with the standard adult weight-status range.
What BMI measures — and what it doesn't
Body mass index divides weight by the square of height to give a single number used as a population-level screening measure, not a diagnosis. It does not distinguish muscle from fat, so athletes and very muscular people are often classed as "overweight" despite low body fat, and it may under-read risk in older adults with reduced muscle mass.
The standard adult ranges
- Below 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25 to 29.9 — overweight
- 30 and above — obesity range
These bands come from World Health Organization guidance for adults and aren't adjusted for age, sex, or ethnicity — treat the result as a starting point for a conversation with a healthcare provider, not a verdict.
Frequently asked questions
What is a healthy BMI?
For most adults, the World Health Organization defines a healthy BMI as 18.5 to 24.9. This range applies to the general adult population and isn't adjusted for muscle mass, frame size, age, or sex.
Is BMI accurate for athletes or muscular people?
Not reliably. Because BMI only uses height and weight, it can't distinguish muscle from fat — a muscular athlete can show as "overweight" on the BMI scale despite having low body fat. Body fat percentage or waist measurements are often more informative for muscular individuals.
Does BMI work the same way for children?
No. Children and teens are assessed using age- and sex-specific BMI percentile charts rather than the fixed adult ranges used here, since healthy body composition changes significantly during growth. This calculator is for adults.
How is BMI calculated?
Metric: weight in kilograms divided by height in meters squared. Imperial: weight in pounds divided by height in inches squared, multiplied by 703. Both formulas give the same result — this tool calculates either depending on the units you pick.