BMI Calculator
Calculate Body Mass Index with category classification.
About this tool
BMI is the most widely used screening tool for weight categories. Enter your weight and height, and instantly see where you fall on the WHO scale — from underweight to obese.
How the BMI Calculator works
The BMI (Body Mass Index) Calculator computes your body mass index using the formula: weight (kg) ÷ height² (m²). It classifies the result into WHO categories: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), and Obese (30+).
How to use this tool
- Enter your weight in kilograms.
- Enter your height in centimeters.
- Click 'Calculate' to see your BMI value and category.
Common use cases
Getting a quick health screening metric
Tracking weight changes over time as part of a fitness plan
Understanding weight categories for insurance or medical forms
Starting a conversation with a healthcare provider about weight management
Examples
- A person weighing 70 kg at 175 cm has a BMI of 22.9 — within the normal range.
- A person weighing 90 kg at 165 cm has a BMI of 33.1 — in the obese category.
Tips & best practices
- BMI is a screening tool, not a diagnosis. It does not distinguish between muscle and fat, so very muscular individuals may be misclassified.
- Track BMI trends over time rather than fixating on a single measurement.
- Combine BMI with waist circumference and other health markers for a more complete picture.
- BMI thresholds were developed from European population data — some Asian populations have higher health risks at lower BMIs.
Common mistakes to avoid
❌ Using pounds instead of kilograms or inches instead of centimeters — the tool expects metric units. Convert first: 1 lb = 0.4536 kg, 1 inch = 2.54 cm.
❌ Treating BMI as a definitive health assessment — it is one data point among many and works best at the population level.
❌ Applying adult BMI categories to children or teenagers — pediatric BMI uses age- and sex-specific percentiles.
Frequently Asked Questions
What BMI range is considered healthy?
18.5 to 24.9 is generally classified as normal for adults. Below 18.5 is underweight; 25-29.9 is overweight; 30+ is obese.
Is BMI a medical diagnosis?
No. BMI is a screening metric, not a clinical diagnosis. It does not account for muscle mass, bone density, or fat distribution.
Why is BMI less accurate for athletes?
Athletes have higher muscle mass which weighs more than fat, so their BMI may appear in the overweight range despite very low body fat.
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