Body Mass Index (BMI) Calculator

HealthLast updated: August 17, 2026

Body mass index (BMI) is the most widely used measure of whether your weight sits in a healthy range for your height. It is found by dividing body weight in kilograms by the square of height in meters, and it is read against the thresholds the World Health Organization (WHO) defines for adults.

This calculator returns your BMI, shows your category under the WHO classification, and gives the ideal weight range for your height in kilograms (a BMI of 18.5-24.9). If you fall outside that range, it also tells you how many kilograms above or below it you are.

kg
cm
Enter your height in centimeters (e.g. 175 for 1.75 m).

BMI Reference Ranges

Body mass index does not involve a "rate" but the classification thresholds the World Health Organization defines for adults. This calculator uses the ranges below, and the healthy weight band is derived from the 18.5 and 24.9 bounds.

Underweight
Below 18.5
A range that should be assessed for undernutrition, muscle loss, and weakened immunity
Normal (healthy)
18.5 – 24.9
The healthy weight range for your height is computed from these two thresholds
Overweight
25.0 – 29.9
The pre-obesity range in which cardiovascular risks begin to rise
Obese — Class I
30.0 – 34.9
Obese — Class II
35.0 – 39.9
Obese — Class III
40.0 and above
Also called morbid obesity

The adult classification the WHO published in 2000, which is still in forceKaynak: World Health Organization (WHO) — Adult BMI classification

Formula

BMI = Weight (kg) / Height² (m²)
Example: 70 / (1.75 × 1.75) = 22.9
Ideal weight range = 18.5 × Height² to 24.9 × Height²

The most common mistake is squaring the height in centimeters; the formula uses height in meters (175 cm = 1.75 m).

How to Calculate

  1. Enter your weight in kilograms (decimals are accepted, e.g. 72.5).
  2. Enter your height in centimeters (e.g. 168 for 1.68 m).
  3. Read your BMI and your WHO category in the results section.
  4. Use the ideal weight range row to see the healthy weight band for your height, and the status row to see how far above or below it you are.

Worked Examples

An example inside the normal range

For 70 kg and 175 cm, BMI = 70 / 1.75² = 22.9, which falls in the 'Normal' category. The ideal weight range for this height is 56.7 - 76.3 kg.

Body mass index (BMI): 22.9 · WHO category: Normal · Your ideal weight range: 56.7 – 76.3 kg

An example above the healthy range

For 90 kg and 170 cm the BMI is 31.1, which falls in the 'Obese (Class I)' category. Since the ideal range is 53.5 - 72.0 kg, the excess is about 18.0 kg.

Body mass index (BMI): 31.1 · WHO category: Obese (Class I) · Your ideal weight range: 53.5 – 72.0 kg

An example in the underweight category

For 50 kg and 168 cm the BMI is 17.7, which is in the 'Underweight' category. Compared with the lower bound of the ideal range (52.2 - 70.3 kg), the shortfall is about 2.2 kg.

Body mass index (BMI): 17.7 · WHO category: Underweight · Your ideal weight range: 52.2 – 70.3 kg

Frequently Asked Questions

What is a healthy BMI?
According to the WHO, the healthy range for adults is 18.5 to 24.9. A BMI of 25.0 to 29.9 is classified as overweight, 30 and above as obese, and below 18.5 as underweight. These thresholds are the same for women and men.
Can BMI be misleading for athletes?
Yes. BMI does not distinguish fat mass from muscle mass, so athletes with a high proportion of muscle can appear 'overweight' while being perfectly healthy. In those cases, body fat percentage and waist circumference give a more accurate picture.
Is BMI interpreted the same way in children?
No. Between the ages of 2 and 18, BMI is assessed against age- and sex-specific percentile curves; adult thresholds such as 18.5-24.9 do not apply to children. This calculator is designed for adults.
How is the ideal weight range calculated?
Your height in meters is squared and then multiplied by the healthy BMI bounds of 18.5 and 24.9. For a height of 1.75 m, for example, the ideal range runs from 18.5 × 3.0625 = 56.7 kg to 24.9 × 3.0625 = 76.3 kg.
My BMI is normal but I carry belly fat; is that a problem?
It can be. BMI looks at total weight and says nothing about where the fat is stored. Fat around the abdomen (a waist circumference above 102 cm in men or 88 cm in women) carries metabolic risk even when BMI is normal.
Is BMI used during pregnancy?
The standard BMI classification does not apply in pregnancy, because weight naturally increases. Pre-pregnancy BMI is used to set the recommended weight gain, and the follow-up is handled by an obstetrician.