BMI Calculator - Body Mass Index Calculator
Calculate your Body Mass Index (BMI) and determine if you are underweight, normal weight, overweight, or obese. Free, accurate BMI calculator with imperial and metric units.
About BMI (Body Mass Index)
Body Mass Index (BMI) is a simple calculation using your height and weight to determine if your weight falls within a healthy range. The formula was developed in the 1800s by Belgian statistician Adolphe Quetelet and has become a widely-used screening tool by healthcare professionals worldwide.
How is BMI Calculated?
BMI is calculated using the formula: weight (kg) / height (m)² for metric units, or (weight (lbs) / height (in)²) × 703 for imperial units. The resulting number is then classified into categories:
- Underweight: BMI less than 18.5
- Normal weight: BMI between 18.5 and 24.9
- Overweight: BMI between 25 and 29.9
- Obese: BMI of 30 or greater
Limitations of BMI
While BMI is a useful screening tool, it has important limitations that you should be aware of:
- Doesn't distinguish between muscle and fat: Athletes and very muscular individuals may have high BMIs despite being healthy and having low body fat.
- Doesn't account for body fat distribution: BMI doesn't tell you where fat is stored. Abdominal fat carries higher health risks than fat stored elsewhere.
- Age and sex differences: BMI doesn't account for natural variations in body composition between men and women, or changes that occur with aging.
- Ethnic variations: Some research suggests different BMI thresholds may be more appropriate for certain ethnic groups.
What is a Healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, optimal BMI can vary based on factors like age, sex, ethnicity, and individual body composition. Some research suggests slightly different ranges may be healthier for certain populations. For example, Asian populations may have higher health risks at lower BMI levels.
Beyond BMI: Other Health Measures
BMI is just one tool for assessing health. Consider these additional measures for a more complete picture:
- Waist circumference: A better indicator of abdominal fat and health risks
- Body fat percentage: More accurate than BMI for assessing body composition
- Waist-to-hip ratio: Helpful for assessing fat distribution patterns
- Blood pressure and cholesterol: Direct measures of cardiovascular health
- Physical fitness: Strength, endurance, and flexibility are important health markers
When to See a Healthcare Provider
Always consult healthcare professionals for comprehensive health assessments. BMI is a screening tool, not a diagnostic tool. If your BMI suggests you may be underweight or overweight, talk to your doctor about whether you should make changes and how to do so safely. They can consider your full health picture, including family history, lifestyle factors, and other health markers.