BMI Calculator — Free Body Mass Index Tool
Calculate your Body Mass Index based on height and weight. See your BMI category instantly. Free online health calculator.
BMI Categories
BMI Calculator — Free Body Mass Index Calculator
Calculate your Body Mass Index instantly by entering your height and weight. BMI is a widely used screening tool that provides a quick estimate of body fat based on your physical measurements. It is used by healthcare professionals, insurance companies, and fitness programs worldwide.
The BMI formula divides your weight in kilograms by the square of your height in meters (kg/m²). This calculator supports both metric and imperial units and automatically categorizes your result into underweight, normal weight, overweight, or obese ranges based on WHO guidelines.
BMI calculators are commonly used during routine health checkups, when applying for health or life insurance, for military and law enforcement fitness assessments, and as a starting point for personal fitness goals. Schools and public health organizations also use BMI for population-level health monitoring.
How the BMI Calculator Works
- Enter your height (in cm or feet/inches)
- Enter your weight (in kg or lbs)
- Your BMI is calculated instantly
- See which category your BMI falls into (underweight, normal, overweight, obese)
Understanding BMI
Body Mass Index (BMI) is a screening tool that estimates body fat based on height and weight. A BMI of 18.5-24.9 is considered normal weight. BMI has limitations: it doesn't distinguish between muscle and fat, so athletes may show as overweight despite being healthy. It also doesn't account for age, gender, or body composition. Use BMI as a starting point, not a definitive health assessment.
When to Use a BMI Calculator
Use this calculator for a quick health screening to understand where your weight falls relative to your height. Doctors use BMI as an initial indicator during checkups, and it is commonly required for health insurance applications, military fitness assessments, and immigration medical exams. Keep in mind that BMI does not distinguish between muscle and fat — athletes may show a high BMI despite being very fit.
Common Use Cases
- •Quick health screening to understand where your weight falls relative to your height
- •Health insurance applications and military fitness assessments that require BMI
- •Tracking BMI changes over time as part of a weight management program
- •Educational tool for health classes and nutrition courses
Expert Tips
- ✱BMI does not distinguish between muscle and fat — athletes should use body fat percentage for a more accurate assessment
- ✱Combine BMI with waist-to-hip ratio for a more complete picture of health risk factors
- ✱For children and teenagers, use BMI-for-age percentile charts instead of standard adult BMI categories
Frequently Asked Questions
- BMI = weight (kg) / height (m)^2. For imperial units: BMI = (weight in pounds x 703) / (height in inches)^2. For example, a person weighing 70 kg at 1.75 m tall has a BMI of 70 / (1.75 x 1.75) = 22.9, which falls in the normal weight range.
- The WHO classifies BMI as: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), Obesity Class I (30-34.9), Obesity Class II (35-39.9), and Obesity Class III (40+). These ranges were developed from population studies linking BMI to health outcomes.
- BMI can be misleading for muscular individuals because muscle weighs more than fat. A bodybuilder might have a BMI of 30 (classified as obese) while having very low body fat. For athletes, body fat percentage, waist circumference, or DEXA scans provide more accurate assessments.
- For adults 20 and older, the standard BMI ranges apply regardless of age. For children and teens (2-19), BMI is interpreted using age- and sex-specific percentiles because body composition changes with growth. A pediatrician can help interpret BMI-for-age charts.
- Yes, it is completely free. All calculations happen in your browser — your height and weight data are never sent to any server or stored anywhere.
What is the formula for BMI?▾
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