Free BMI Calculator Online
BMI with WHO risk classification, ideal weight & body fat estimate
BMI (Body Mass Index) is a widely used screening tool that relates your weight to your height to estimate whether you fall within a healthy weight range. This calculator applies the WHO classification system, giving you both your numeric score and the associated health risk category. It's useful for adults tracking weight health, though it works best alongside other measurements like waist circumference or body fat percentage.
Frequently Asked Questions
About the BMI Calculator
Body Mass Index was developed in the 1830s by mathematician Adolphe Quetelet as a population-level statistical tool — not as a diagnostic for individuals. Despite this, it became a clinical standard because it requires only a scale and a tape measure, making it accessible everywhere from clinics to home use.
The WHO classification thresholds (underweight below 18.5, normal 18.5–24.9, overweight 25–29.9, obese 30+) are based on population-level studies of cardiovascular and metabolic risk. They are a useful starting point, but they don't account for muscle mass, bone density, age, or how fat is distributed across the body.
Use your BMI result as one data point among several. Pairing it with waist circumference (a better predictor of visceral fat) and body fat percentage gives a much fuller picture of your metabolic health.
Formula Used
BMI = weight(kg) / height(m)²
For imperial: BMI = 703 × weight(lbs) / height(in)²
When Should You Use This?
Use this calculator as a quick, first-step screening tool to determine if your weight falls into a healthy range for your height according to the World Health Organization.
What Does The Result Mean?
Your BMI score places you into a category (Underweight, Normal, Overweight, or Obese). The results indicate your statistical risk for weight-related diseases.
Example Calculation
Calculating BMI for a 35-year-old woman (metric)
📥 Inputs
- Weight: 68 kg
- Height: 1.65 m
🔢 Calculation Steps
- 1Square the height: 1.65 × 1.65 = 2.7225 m²
- 2Divide weight by height squared: 68 ÷ 2.7225 = 24.98
- 3Round to one decimal: BMI = 25.0
- 4WHO category: Overweight (25.0–29.9) — borderline, just above Normal
Limitations of this Calculator
- BMI cannot distinguish between muscle mass and fat mass. Bodybuilders will often score as "Obese".
- It does not account for age, bone density, or how fat is distributed (visceral vs subcutaneous fat).
How to Use the BMI Calculator
- 1Select your preferred measurement system (Metric or Imperial).
- 2Enter your current weight.
- 3Enter your height.
- 4Instantly see your BMI score, WHO category, and ideal weight range.
Tips & Best Practices
- BMI does not distinguish between muscle and fat. Highly muscular individuals may be classified as 'overweight' despite having low body fat.
- Double-check your input units before calculating — using the wrong unit is the most common source of errors.
- Bookmark this BMI Calculator for quick access next time you need it.
- Use the share button to send your results to a colleague or save them for later reference.
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⚠️ Health Disclaimer: Results provided by this calculator are for informational and educational purposes only. They do not constitute medical advice. Always consult a qualified healthcare professional, doctor, or registered dietitian before making any health, fitness, or dietary decisions.