Know your
Body Mass Index.
Calculate your BMI from height and weight in metric or imperial units. See your WHO category, healthy weight range, and BMI prime — all in seconds.
BMI Categories.
Body Mass Index categories for adults aged 20 and older, as defined by the World Health Organization.
| Category | BMI Range (kg/m²) | Health Risk |
|---|---|---|
| Underweight | Below 18.5 | Moderate risk of nutritional deficiency and osteoporosis |
| Normal Weight | 18.5 – 24.9 | Lowest risk of weight-related health problems |
| Overweight | 25.0 – 29.9 | Increased risk of cardiovascular disease and diabetes |
| Obese Class I | 30.0 – 34.9 | High risk of type 2 diabetes and hypertension |
| Obese Class II | 35.0 – 39.9 | Very high risk of serious health conditions |
| Obese Class III | 40.0 and above | Extremely high risk; seek medical advice |
Calculate your BMI in 3 steps.
Choose Your Units
Switch between metric (cm / kg) and imperial (ft / lb). The calculator converts everything to a single formula internally.
Enter Height & Weight
Type your height and weight. The results update in real time — no button to press. Your BMI appears immediately.
Read Your Results
Get your BMI score, WHO category, healthy weight range for your height, and BMI Prime — all in one view.
The BMI Formula
The Body Mass Index is calculated using one of two formulas depending on the unit system:
Frequently Asked Questions.
BMI (Body Mass Index) is a numerical value calculated from a person's weight and height. It is widely used as a screening tool to categorize whether an adult is underweight, at a healthy weight, overweight, or obese.
In metric units, BMI = weight (kg) ÷ height² (m²). In imperial units, BMI = 703 × weight (lb) ÷ height² (in²). Our calculator supports both systems and converts automatically.
According to the World Health Organization (WHO): Underweight is below 18.5; Normal weight is 18.5–24.9; Overweight is 25.0–29.9; Obese Class I is 30.0–34.9; Obese Class II is 35.0–39.9; Obese Class III is 40.0 and above.
BMI is a useful screening tool for most adults, but it has limitations. It does not distinguish between muscle and fat, so athletes may have a high BMI without excess body fat. It is also less accurate for the elderly, pregnant women, and children. Always consult a healthcare professional for a full assessment.
For most adults aged 20 and older, a healthy BMI range is 18.5 to 24.9. This range is associated with the lowest risk of weight-related health problems.
BMI Prime is the ratio of your BMI to the upper limit of the healthy range (25). A BMI Prime below 1.0 means you are within the healthy range; above 1.0 indicates overweight. For example, BMI 22.5 → BMI Prime 0.90.
Yes, the BMI calculator is 100% free with no signup, no downloads, and no hidden costs.