How to Calculate BMI
Body Mass Index (BMI) is a simple screening number based on your height and weight. It helps you quickly see whether your weight falls into an underweight, healthy, overweight, or obese range.
Step-by-step
- 1
Measure your weight
Record your weight in kilograms (metric) or pounds (imperial).
- 2
Measure your height
Record your height in meters or centimeters (metric) or inches (imperial).
- 3
Apply the BMI formula
Divide weight by height squared, then multiply by 703 if using pounds and inches.
- 4
Interpret your result
Compare your BMI against the standard adult categories to see your weight range.
The BMI formula
In metric units, BMI = weight (kg) ÷ height² (m²). In imperial units, BMI = (weight (lbs) ÷ height² (in²)) × 703. The two formulas are equivalent and produce the same result when units are converted correctly.
Worked example
For a person who weighs 70 kg and is 1.75 m tall: 1.75² = 3.0625, then 70 ÷ 3.0625 = 22.9. A BMI of 22.9 falls within the healthy range of 18.5–24.9.
What BMI does and doesn't tell you
BMI is a useful screening tool but does not measure body fat directly. Highly muscular people can have a high BMI with low body fat, while some people with a healthy BMI may still carry excess fat. Use it as a starting point, not a diagnosis.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.
Is BMI different for men and women?
The formula is the same, but interpretation can differ because men often carry more muscle mass, which can raise BMI without excess fat.
Can I calculate BMI in pounds and inches?
Yes. Use the imperial formula: BMI = (weight in pounds ÷ height in inches squared) × 703.