BMI Calculator Guide: Formula, Categories, and Limits
BMI, or Body Mass Index, is a quick screening number based on height and weight. It can be useful, but it is not a diagnosis and does not measure body fat directly.
Enter height and weight to estimate BMI.
Open the BMI CalculatorBMI Formula
Metric: BMI = weight in kilograms / height in meters squared.
US units: BMI = 703 x weight in pounds / height in inches squared.
Example: If someone weighs 170 lb and is 70 inches tall, BMI = 703 x 170 / 70² = 24.4.
BMI Categories
- Underweight: below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obesity: 30 or higher
These categories are common for adults, but the meaning can vary by age, sex, ethnicity, muscle mass, pregnancy, and health history. A BMI calculator is best used as a starting point, not the final word.
When BMI Can Be Misleading
Athletes may have a high BMI because muscle weighs more than fat. Older adults may have a “normal” BMI while still having low muscle mass. Children and teens need age-and-sex-specific BMI percentiles instead of adult ranges.
Useful BMI Searches
People often look for BMI calculator, body mass index calculator, healthy weight calculator, BMI chart, ideal weight calculator, overweight calculator, and BMI formula. A good page answers those questions without pretending BMI is more precise than it is.
FAQ
Is BMI accurate?
BMI is a useful screening tool, but it does not measure body fat, muscle, or overall health directly.
What BMI is considered normal?
For many adults, 18.5 to 24.9 is commonly classified as normal weight.
Should I use BMI for medical decisions?
No. Use BMI as general information and speak with a qualified healthcare professional for personal advice.