Body mass index (BMI) calculator
Enter weight in kilograms and height in centimetres. The tool calculates BMI as weight divided by height squared and shows the corresponding adult reference category.
Calculate BMI
BMI is a population-level screening measure, not a diagnosis or a personal health target. This calculator is for adults; do not use these adult cutoffs for children or teenagers. Pregnancy and individual circumstances need professional assessment.
WHO adult reference categories
| BMI | WHO adult reference category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Reference range |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obesity class I |
| 35.0–39.9 | Obesity class II |
| 40.0 or above | Obesity class III |
What BMI can and cannot tell you
- BMI is calculated from weight and height. It does not directly measure body fat or distinguish fat from muscle, so it may not describe an individual’s health on its own.
- The World Health Organization presents the standard adult categories for adults over 20 years old. Children and adolescents need age- and sex-specific growth references rather than these adult cutoffs.
- A BMI value is not a diagnosis and does not establish that a person is healthy or unwell. Pregnancy, body composition, age and medical history can affect interpretation. Discuss personal questions with a qualified health professional.
How the calculation works
Height is converted from centimetres to metres. BMI = weight in kilograms ÷ (height in metres × height in metres). The displayed weight interval is the arithmetic range corresponding to BMI 18.5 through 24.9 for the entered height, rounded to one decimal place. It is a reference calculation, not an individualized goal.
Frequently asked questions
Is BMI a diagnosis?
No. It is a screening measure based on weight and height. A single BMI value cannot diagnose a condition or describe someone’s full health.
Can I use these ranges for a child or teenager?
No. WHO uses age- and sex-specific growth references for children and adolescents. The adult cutoffs on this page are not intended for them.
Why can BMI be misleading for some adults?
The formula does not separate muscle from fat and does not include every factor relevant to health. A clinician can interpret it alongside other information.
Is the calculated weight interval my ideal weight?
No. It is only the weight interval that mathematically corresponds to the adult BMI reference range at the entered height. It is not a personal target or medical recommendation.
Can I use BMI during pregnancy?
This calculator does not assess weight gain during pregnancy. Ask a prenatal care professional about individual measurements and guidance.
Sources and further reading
Adult reference categories and the BMI definition are based on World Health Organization information. The WHO growth reference for ages 5–19 is listed separately because adult cutoffs are not used for children and adolescents.