BMI Calculator
Find your Body Mass Index (BMI) based on your height and weight, and see how it compares to standard weight categories.
Your BMI will appear here
Enter your weight and height, then click calculate to see your BMI and category.
Quick Answer
BMI is calculated by dividing your weight by the square of your height (kg/m², or lb/in² × 703). A BMI between 18.5 and 24.9 is considered a healthy weight for most adults.
How It Works: Formula & Variables
BMI = weight (kg) / height (m)²
BMI = weight (lb) / height (in)² × 703
- Underweight
- BMI below 18.5
- Healthy weight
- BMI 18.5 – 24.9
- Overweight
- BMI 25.0 – 29.9
- Obesity
- BMI 30.0 and above
Worked Examples
Example 1: Imperial units
A person weighing 160 lb at 5'9" (69 inches): BMI = (160 / 69²) × 703 = 23.6, which falls in the healthy weight range.
Example 2: Metric units
A person weighing 73 kg at 175 cm (1.75 m): BMI = 73 / 1.75² = 23.8, also in the healthy weight range.
Key Concepts
BMI categories: BMI groups people into underweight, healthy weight, overweight, and obesity categories based on weight relative to height.
A screening tool, not a diagnosis: BMI is useful for spotting general trends across populations, but it doesn't directly measure body fat or account for muscle mass.
Limitations: Athletes, older adults, and people with different body compositions may have a BMI that doesn't reflect their actual health status.
Common Mistakes
Treating BMI as a complete health picture: BMI doesn't account for factors like waist circumference, muscle mass, or overall fitness.
Mixing up units: Make sure to enter height and weight consistently in either imperial or metric units.
Applying adult categories to children: BMI for children and teens should be assessed using age- and sex-specific growth charts, not the adult categories shown here.
Frequently Asked Questions
BMI (Body Mass Index) is a measure that uses your height and weight to estimate whether your weight is in a healthy range for your height. It's calculated by dividing your weight by the square of your height.
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is considered underweight, 25.0–29.9 is overweight, and 30.0 or above is classified as obesity.
BMI is a useful general screening tool, but it doesn't account for muscle mass, bone density, body composition, or distribution of fat. Athletes and very muscular people, for example, may have a high BMI without excess body fat.
For imperial units, BMI = (weight in pounds / (height in inches)²) × 703. For metric units, BMI = weight in kilograms / (height in meters)².
No. BMI for children and teens is interpreted differently, using age- and sex-specific percentile charts rather than the fixed adult categories used here. This calculator is intended for adults.