Body Mass Index (BMI) is a number derived from your height and weight that estimates whether your weight is in a healthy range for your height. The formula is the same worldwide: weight divided by the square of height. Metric units use kilograms and metres; imperial units use pounds and inches with a conversion factor of 703.
This calculator supports both unit systems. In metric mode you enter height in centimetres and weight in kilograms. In imperial mode you can enter height either as total inches or as feet and inches, and weight in pounds. The result is rounded to one decimal place and paired with the standard WHO category: underweight, normal, overweight, or obese.
BMI is a screening tool, not a diagnosis. It doesn't distinguish between muscle and fat, so very muscular people can register as overweight without being unhealthy. Use it as a starting point and consult a healthcare professional for personal advice. For most adults, a BMI between 18.5 and 24.9 is considered a healthy range.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These ranges are based on World Health Organization guidance.
How is BMI calculated?
BMI equals weight in kilograms divided by height in metres squared (kg/m²). For imperial units, the formula is 703 × weight in pounds ÷ height in inches squared. The calculator applies the correct formula based on your selected units.
Is BMI accurate for everyone?
BMI is a useful screening measure but has limits. It doesn't account for muscle mass, bone density, or fat distribution, so athletes and older adults may get misleading results. Treat it as a starting point, not a definitive health measure.
Can I use feet and inches?
Yes. Switch the units dropdown to Imperial and use the feet and inches fields. The calculator converts them to total inches before applying the imperial BMI formula.