Body Mass Index — weight in kilograms divided by height in meters squared — has been the standard population-level screening measure for weight categories since the 1970s. The WHO ranges classify a BMI under 18.5 as underweight, 18.5–24.9 as normal, 25–29.9 as overweight, and 30+ as obese.
This calculator computes BMI from metric or imperial units and shows where the result falls on the WHO scale. Remember that BMI is a screening tool, not a diagnosis: it cannot distinguish muscle from fat and should be interpreted alongside other health measures, ideally with a healthcare professional.
How to Use This Tool
- Choose metric (kg, cm) or imperial (lb, ft/in) units.
- Enter your weight and height.
- Read your BMI and its WHO category instantly.
- Track the value over time rather than fixating on a single reading.
Frequently Asked Questions
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so muscular people frequently register as 'overweight' with low body fat. For athletes, waist circumference, body-fat percentage, and fitness markers are far more informative than BMI alone.
Does the same scale apply to children?
No. Children and teens use age- and sex-specific BMI percentiles rather than fixed cutoffs, because healthy body composition changes throughout growth. Pediatric growth charts are the right reference there.
What are BMI's main limitations?
It ignores muscle mass, fat distribution (visceral fat is riskier than subcutaneous), bone density, age, and ethnicity — several health bodies use adjusted cutoffs for some populations. Treat it as one coarse signal among many, not a verdict on health.