BMI Calculator: Calculate Your Body Mass Index

Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on height and weight. Our free BMI Calculator supports both metric and imperial units and shows your BMI category, a visual scale, and your healthy weight range.

How to Use the Calculator

Choose your unit system: Metric (kg/cm) or Imperial (lb/ft/in)
Enter your weight: In kilograms or pounds
Enter your height: In centimeters, or feet and inches
Click Calculate: See your BMI value, category, and healthy weight range

Understanding BMI Categories

BMI Range	Category
Below 18.5	Underweight
18.5 - 24.9	Normal weight
25.0 - 29.9	Overweight
30.0 - 34.9	Obese (Class I)
35.0 - 39.9	Obese (Class II)
40.0 and above	Obese (Class III)

The BMI Formula

Metric: BMI = weight (kg) / height (m)^2

Imperial: BMI = 703 x weight (lb) / height (in)^2

For example, a person weighing 70 kg at 175 cm tall: BMI = 70 / (1.75)^2 = 22.9 (Normal weight).

What BMI Tells You

BMI is a screening tool, not a diagnosis. It provides a quick estimate of whether your weight is in a healthy range for your height. The visual scale on the calculator shows where your BMI falls relative to the standard categories.

The calculator also shows your healthy weight range — the weight range that corresponds to a BMI of 18.5-24.9 for your height.

Limitations of BMI

BMI does not account for:

Muscle mass: Athletes may have a high BMI due to muscle, not fat
Body composition: Two people with the same BMI can have very different body fat percentages
Age and sex: BMI ranges don’t adjust for age or sex differences
Bone density: People with denser bones may weigh more
Distribution of fat: Where fat is stored matters for health risk

Tips

Use BMI as one data point, not the only measure of health
Track BMI over time to see trends rather than focusing on a single reading
For a more complete picture, combine BMI with waist circumference and body fat percentage
Consult a healthcare professional for personalized health assessment

Frequently Asked Questions

Is BMI accurate for children? This calculator is for adults (18+). Children’s BMI is calculated differently, using age and sex-specific percentiles.

Does BMI apply to pregnant women? BMI during pregnancy is not meaningful for the same categories. Pre-pregnancy BMI is used for clinical guidance.

Why does my doctor still use BMI? Despite its limitations, BMI is a quick, free screening tool that correlates with health risks at the population level.

Try our free BMI Calculator to check your Body Mass Index.