How to Calculate Your BMI (Formula and Free Calculator)
4 min read
Body Mass Index (BMI) is a quick screening number that compares your weight to your height. It is not a perfect measure of health, but it is an easy starting point that doctors and forms often use.
Here is how to calculate your BMI in either metric or imperial units, what the result means, and where BMI falls short.
Step by step
- 1Metric formula
BMI = weight in kilograms divided by height in metres, squared. Example: 70 kg and 1.75 m gives 70 / (1.75 x 1.75) = 22.9.
- 2Imperial formula
BMI = weight in pounds divided by height in inches squared, times 703. Example: 154 lb and 69 in gives 154 / (69 x 69) x 703 = 22.7.
- 3Read your category
Under 18.5 is underweight, 18.5 to 24.9 is a healthy range, 25 to 29.9 is overweight, and 30 or above is in the obese range (for most adults).
- 4Use the calculator
Enter your height and weight in the BMI Calculator to get your number and category instantly, in either unit system.
Tips
- BMI does not distinguish muscle from fat, so very muscular people can read as overweight while being healthy.
- It is a population-level screening tool, not a diagnosis - waist measurement, body composition, and bloodwork tell a fuller story.
- BMI categories differ for children, and cutoffs can vary by ethnicity - treat the standard adult ranges as a rough guide.
Frequently asked questions
What is the BMI formula?
Metric: weight in kg divided by height in metres squared. Imperial: weight in pounds divided by height in inches squared, multiplied by 703.
What is a healthy BMI?
For most adults, 18.5 to 24.9 is considered the healthy range. Below that is underweight; 25 and above is overweight or obese.
Is BMI accurate?
It is a useful quick screen but has real limits - it cannot tell muscle from fat or where weight is carried. Use it alongside other measures and a doctor's advice, not on its own.