BMI Calculator
Free to use. Runs in your browser: your files and text are not uploaded.
This tool gives general information only. It is not medical advice.
Enter your height and weight to get your body mass index, the category it falls in, and the weight range counted as normal for your height.
How to use it
- Choose metric units (cm and kg) or US units (feet, inches and pounds).
- Type your height and weight. The result updates as you type.
The formula
BMI = weight (kg) ÷ height (m)²
In US units: BMI = weight (lb) × 703 ÷ height (in)².
Example: 70 kg and 175 cm. Height in metres is 1.75, and 1.75² = 3.0625. BMI = 70 ÷ 3.0625 = 22.9.
Categories for adults
These are the World Health Organization’s categories for adults aged 20 and over:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
The WHO has noted that health risks appear at lower BMI values in many Asian populations, and some countries use lower cut-offs. In India, for example, guidelines published in 2009 class 23 and above as overweight and 25 and above as obese.
What BMI does not measure
BMI is a screening measure based only on height and weight. It does not measure body fat directly, and it does not show where fat is carried. Waist size gives extra information: the WHO links a waist above 94 cm in men and 80 cm in women with increased risk.
Limits
- The categories apply to adults. Children and teenagers are assessed with age- and sex-specific growth charts.
- BMI does not apply during pregnancy.
- It is less reliable for very muscular people and for older adults who have lost muscle.
- A BMI figure is not a diagnosis. A doctor or nurse can assess your health with more than one number.
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. For 70 kg and 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9.
What is a normal BMI?
For adults, the World Health Organization classes 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or more as obesity. Below 18.5 is underweight.
Is BMI accurate for athletes and older people?
BMI cannot tell muscle from fat. Muscular people can have a high BMI with little body fat, and older people who have lost muscle can have a normal BMI with more fat.