BMI Calculator
A BMI calculator is a free online tool that computes your Body Mass Index from height and weight, showing your category (underweight, normal, overweight, or obese).
How to use BMI Calculator
- Choose units β Pick metric (kg/cm) or imperial (lb/in).
- Enter height & weight β Type your measurements.
- See BMI β View your BMI value and health category.
Key features
- Metric & imperial
- WHO-standard categories
- Instant result
- Mobile-friendly
- Free and private
What is BMI?
Body Mass Index (BMI) is a simple measure that compares a person's weight to their height. Formula: BMI = weight (kg) / heightΒ² (mΒ²). It's used worldwide as a screening tool to categorize adults as underweight, normal weight, overweight, or obese. BMI was developed in the 1830s and remains the most widely used population-level measure of body composition.
BMI Categories (WHO)
The World Health Organization defines these categories: Under 18.5 = Underweight. 18.5-24.9 = Normal weight. 25-29.9 = Overweight. 30+ = Obese. Obese is further divided into Class I (30-34.9), Class II (35-39.9), and Class III (40+). Each category carries different health risk profiles.
Limitations of BMI
BMI doesn't distinguish muscle from fat. A muscular athlete may have a BMI of 28 (classified as 'overweight') while being extremely healthy. Conversely, someone with a 'normal' BMI can have high body fat and low muscle mass. BMI also doesn't account for fat distribution β belly fat is more dangerous than fat on hips and thighs. Use BMI as one of several indicators, not a diagnosis.
Should You Use BMI?
BMI is useful as a quick screening tool for large populations and for tracking changes over time. For personal health decisions, combine BMI with other measures: waist circumference, body fat percentage, blood pressure, and lipid profile. Always consult a healthcare professional for personalized advice.
Pro tips
- BMI is a screening tool, not a diagnosis
- Athletes may have high BMI due to muscle β ignore BMI for them
- Track BMI trends over time rather than a single reading
- Combine BMI with waist circumference for better accuracy
Common use cases
- Quick health screening
- Tracking weight loss progress
- Fitness and nutrition planning
- Medical pre-screening
- Population health research
Frequently asked questions
What is a healthy BMI?+
18.5β24.9 is generally considered healthy by the WHO.
Is BMI accurate?+
It's a rough indicator β doesn't account for muscle mass, bone density, or body composition.
What is a normal BMI range?+
18.5 to 24.9 (normal weight), 25-29.9 (overweight), 30+ (obese), under 18.5 (underweight).
Is it free?+
Yes, 100% free.
Can I calculate BMI for children?+
BMI for children uses age- and sex-specific percentiles, so this adult calculator is not suitable.
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