How BMI Calculator Works
In metric units, BMI is your weight in kilograms divided by the square of your height in metres. In imperial units, it's your weight in pounds multiplied by 703, divided by the square of your height in inches. The result is compared against the standard World Health Organization weight categories.
How to Use This Tool
- Choose metric or imperial units.
- Enter your weight and height.
- Select Calculate BMI to see your BMI value and weight category.
Example
Someone weighing 70 kg at 175 cm tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the Normal weight category.
Helpful Tips
- BMI doesn't distinguish between muscle and fat, so it can overestimate body fat in very muscular people and underestimate it in older adults with less muscle mass.
- Use BMI as a general screening indicator, not a diagnosis — talk to a healthcare provider for a full health assessment.
Frequently Asked Questions
What BMI ranges count as underweight, normal, overweight or obese?
Under 18.5 is Underweight, 18.5–24.9 is Normal weight, 25–29.9 is Overweight, and 30 or above is Obese.
Is BMI accurate for everyone?
It's a useful population-level screening tool, but it doesn't account for muscle mass, bone density, age or sex, so it can be misleading for athletes, older adults and some other groups.
Can I switch between metric and imperial units?
Yes, use the units dropdown at the top of the calculator — the relevant fields will switch automatically.
Is BMI different for children?
Yes, children and teenagers use age- and sex-specific BMI percentile charts rather than the fixed adult categories used here.
This tool runs entirely in your browser. Your input is not uploaded to any server.