BMI Calculator
Calculate your Body Mass Index in seconds and see what it means for your health.
BMI Calculator
Calculate your Body Mass Index instantly.
Your BMI
0.00A BMI calculator gives you a fast, reliable way to check where your weight stands. Enter your height and weight to instantly get your BMI score, weight category, and a healthy range for your exact height — using the same formula doctors and health agencies rely on worldwide.
What Is BMI?
Body mass index is a simple number calculated from your height and weight, used by health organizations to screen for weight-related health risk across large populations.
WHO and CDC both use BMI bands to flag underweight, normal, overweight, or obese ranges. It is not a diagnosis on its own — it's a starting point a doctor can use alongside other measurements for a fuller picture of health.
How the BMI Formula Works
Metric: BMI = Weight (kg) ÷ Height² (m²)
Imperial: BMI = 703 × Weight (lb) ÷ Height² (in²)
Both formulas produce the same BMI score — just different units
This calculator applies the exact formula behind the scenes, so you get a precise result without any manual math or unit conversion.
BMI Chart and Weight Categories
Health agencies divide adult BMI into four standard bands, from underweight to obese, each linked to a different average health risk level.
| Category | BMI Range | Risk Level |
|---|---|---|
| Underweight | Below 18.5 | Increased risk |
| Normal Weight | 18.5 – 24.9 | Lowest risk |
| Overweight | 25 – 29.9 | Moderate risk |
| Obese — Class 1 | 30 – 34.9 | High risk |
| Obese — Class 2 | 35 – 39.9 | Very high risk |
| Obese — Class 3 | 40 and above | Extremely high risk |
Limitations of BMI
BMI is fast and needs no equipment, but has real limitations. A muscular person can register as overweight despite low body fat, and older adults or pregnant women may not fit standard categories.
Remember: Treat BMI as a screening number, not a verdict. Body composition, waist circumference, and activity level all shape your actual health risk.
Why Use the Toolnix BMI Calculator
Frequently Asked Questions
A BMI between 18.5 and 24.9 is considered healthy for most adults, per WHO and CDC guidelines.
Yes. Muscle weighs more than fat by volume, so muscular people can register as overweight despite very low body fat.
This tool is built for adults 18+. Children and teens need age- and gender-specific BMI-for-age growth charts.
No. BMI compares weight to height only, and doesn't measure fat, muscle, or bone density directly.
Every few months is enough for most people — daily checks won't meaningfully change your category.