BMI Calculator
Enter your height and weight — your BMI updates as you type. This tool gives a general estimate based on the standard formula; it is not medical advice or a diagnosis.
How this calculator works
BMI (Body Mass Index) is a simple weight-to-height ratio: metric BMI is weight in kilograms divided by height in meters squared, and imperial BMI is 703 × weight in pounds ÷ height in inches squared. The result is scored against the WHO/CDC adult categories — under 18.5 underweight, 18.5–24.9 normal weight, 25–29.9 overweight, and 30 or above obese. Being honest about its limits: BMI cannot distinguish muscle from fat, so it can misclassify very muscular people as overweight and very lean, low-muscle people as normal, and it doesn't adjust for age, sex, or individual body composition. Use it as a fast, general screening estimate, not a diagnosis.
Worked example
A person weighing 70 kg at 175 cm has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the WHO normal weight band (18.5–24.9).
Frequently asked questions
Is BMI accurate for everyone?
No. BMI only compares your weight to your height — it can't tell muscle from fat. A muscular athlete or a dedicated weightlifter can land in the "overweight" band on BMI alone despite having low body fat, while a very lean person with little muscle can score "normal" despite a higher fat percentage. Treat BMI as a quick population-level screening number, not a verdict on your individual body composition.
What's a healthy BMI range?
The World Health Organization defines 18.5–24.9 as the "normal weight" band for adults, with under 18.5 classed as underweight, 25–29.9 as overweight, and 30 or above as obese. These bands are population averages and don't adjust for age, sex, or muscle mass.
Does BMI work differently for kids?
Yes. Pediatric and teen BMI is plotted on age- and sex-specific growth percentile charts rather than the fixed adult cutoffs used here, because healthy body composition changes a lot during growth. This calculator is built for adults and doesn't cover that scoring — ask a pediatrician for a child's BMI percentile.
Should I make health decisions based on BMI alone?
No. This tool returns a general estimate, not medical advice or a diagnosis. BMI is one rough screening signal among many — it says nothing about where fat is distributed, your muscle mass, blood markers, or overall health. For an actual assessment of your health, talk to a doctor, who can look at the fuller picture.