BMI Calculator – Body Mass Index (Metric & Imperial)

What is BMI?

Body mass index (BMI) compares your weight with your height. It's used worldwide as a quick way to check whether a person's weight is in a healthy range for adults. It's simple to calculate and doesn't need any special equipment.

The BMI formula

BMI = weight (kg) ÷ height (m)²

BMI = 703 × weight (lb) ÷ height (in)²

Example

Someone who is 175 cm tall and weighs 70 kg has a BMI of 70 ÷ 1.75² = 22.9, which is in the healthy range.

BMI categories for adults

BMI	Category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25 – 29.9	Overweight
30 – 34.9	Obesity class I
35 – 39.9	Obesity class II
40 and above	Obesity class III

Limitations of BMI

BMI doesn't measure body fat directly. Athletes with a lot of muscle may be classed as overweight, and people who have lost muscle may look healthy by BMI while carrying too much fat. Use it alongside other measures such as waist circumference or our body fat calculator, and talk to a doctor about your health.

Frequently asked questions

What is a healthy BMI?

For most adults, a BMI from 18.5 to 24.9 is considered a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or higher is in the obese range.

Is BMI accurate?

BMI is a quick screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so very muscular people can have a high BMI while being healthy, and it can underestimate body fat in older adults. Waist size and body fat percentage give extra context.

Does BMI work for children?

No. Children and teenagers are still growing, so their BMI is compared with percentiles for their age and sex. This calculator is designed for adults aged 20 and over.

What is BMI Prime?

BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value between 0.74 and 1.0 is in the healthy range, and a value of 1.2 means you're 20% above the upper limit.