BMI Categories:
- Below 18.5: Underweight
- 18.5 to 24.9: Normal weight
- 25.0 to 29.9: Overweight
- 30.0 to 34.9: Obesity (Class 1)
- 35.0 to 39.9: Obesity (Class 2)
- 40.0 and above: Severe Obesity (Class 3)
Note: BMI is a screening tool and not a diagnostic of body fatness or health. The same BMI may not correspond to the same degree of fatness in different individuals.
BMI Calculator: Find Your Body Mass Index in Seconds
This BMI calculator helps you find your body mass index quickly. Just enter your height and weight below, and the calculator will show your BMI and what it means for your health.
How to Use This BMI Calculator
- Enter your weight in the first box
- Select pounds (lb) or kilograms (kg)
- Enter your height
- Select centimeters (cm), feet, or inches
- Click the "Calculate BMI" button
Your BMI result appears instantly, along with your BMI category (underweight, normal weight, overweight, or obese).
Understanding the BMI Formula
The BMI calculator uses a simple math formula to work out your body mass index:
- For metric units (kg, m): BMI = weight (kg) ÷ height² (m²)
- For imperial units (lb, in): BMI = (weight (lb) × 703) ÷ height² (in²)
The calculator does all this math for you automatically. Just enter your height and weight, and it shows your BMI right away.
BMI Categories and What They Mean
Your BMI result falls into one of these categories:
| BMI Range | Category | What It Means |
|---|---|---|
| Below 18.5 | Underweight | You may need to gain weight |
| 18.5 - 24.9 | Normal weight | Healthy weight range |
| 25.0 - 29.9 | Overweight | You may need to lose some weight |
| 30.0 and above | Obese | You may need to lose weight for health reasons |
The calculator shows which category you fall into based on your BMI result.
BMI for Adults vs. Children
This calculator works best for adults aged 20 and older. For children and teens (ages 2-19), BMI is calculated the same way, but the results are interpreted differently:
- Adults: BMI is compared to fixed categories
- Children: BMI is converted to a percentile based on age and gender
If you're checking a child's BMI, make sure to use a BMI percentile calculator made for children, which considers these important differences.
Steps to Calculate Your BMI
- Measure your height accurately (without shoes)
- Weigh yourself (ideally in the morning, with minimal clothing)
- Enter these numbers in the calculator fields above
- Choose the right units (pounds/inches or kilograms/meters)
- Click the "Calculate" button
- View your BMI result and category in the results section
The calculator handles all unit conversions automatically, so you don't need to convert measurements yourself.
Interesting Facts About BMI
- BMI was created in the 1830s by Belgian mathematician Adolphe Quetelet
- It was originally called the "Quetelet Index" before becoming known as BMI
- BMI doesn't measure body fat directly
- Athletes often have high BMI scores due to muscle mass, not fat
- The healthy BMI range is the same for men and women
- About 39% of adults worldwide have a BMI in the overweight or obese range
- Japan uses different BMI categories than most Western countries
Common Questions About BMI
Using BMI for Men and Women
The BMI formula and categories are the same for both men and women. However, men typically have more muscle mass and less body fat than women at the same BMI.
For example:
- A man with a BMI of 26 might have less body fat than a woman with a BMI of 26
- Women naturally have higher body fat percentages than men
This means BMI should be interpreted alongside other health information for the most accurate picture of your health.
Other Helpful Health Calculators
If you found this BMI calculator useful, you might also like:
- Body fat percentage calculator
- Calorie intake calculator
- Ideal weight calculator
- Waist-to-height ratio calculator
- Metabolic rate calculator
These tools give you a more complete view of your health beyond just BMI.