How to use the BMI calculator
Enter your weight and height in any unit. The other units fill in automatically. Everything stays in sync. Click Clear all to reset and calculate a new person.
What is BMI?
Body Mass Index (BMI) is a simple ratio of weight to height, used since the 1970s as a quick screening tool for weight categories. The formula is:
BMI = weight (kg) ÷ height² (m)
BMI categories
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese Class I | 30.0 – 34.9 |
| Obese Class II | 35.0 – 39.9 |
| Obese Class III | 40.0 and above |
Asian-specific thresholds
| Category | Asian BMI range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 22.9 |
| Overweight | 23.0 – 24.9 |
| Obese I | 25.0 – 29.9 |
| Obese II | 30.0 and above |
What is BMI Prime?
BMI Prime is your BMI divided by 25 — the upper limit of the healthy range. Below 1.0 you're within range. Above 1.0 you're over.
What is the Ponderal Index?
The Ponderal Index is weight (kg) ÷ height³ (m). Unlike BMI, it doesn't over-classify tall people. Useful for very tall or very short individuals.
Limitations of BMI
- It doesn't measure body fat directly. A muscular athlete can have a BMI of 30 with very low body fat.
- It doesn't distinguish where fat is stored. Visceral fat is more harmful than subcutaneous fat.
- It doesn't work well for children. Children use BMI-for-age percentiles.
- It isn't accurate during pregnancy.
Common questions
What is BMI?
Body Mass Index is a measure of body fat based on height and weight.
What is a healthy BMI?
For most adults, 18.5 to 24.9 is healthy. Under the Asian standard, 18.5 to 22.9.
Does BMI work for everyone?
No. It doesn't distinguish muscle from fat. Not accurate for children, pregnant women, or athletes.
Is my data saved?
Your inputs are stored only in your browser's local storage. Nothing is sent to any server.