BMI Calculator - Free Body Mass Index Tool

How the BMI Calculator Works

1. 01Enter your height (in cm or feet/inches)
2. 02Enter your weight (in kg or lbs)
3. 03Your BMI is calculated instantly
4. 04See 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

What is the formula for BMI?→

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.

What are the BMI categories?→

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.

Is BMI accurate for athletes?→

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.

What is a healthy BMI for my age?→

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.

Is this BMI calculator free to use?→

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.