BMI Calculator

Calculate your Body Mass Index (BMI) to assess your weight category based on height and weight. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.

How to Use the BMI Calculator

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a BMI Calculator?

A BMI (Body Mass Index) Calculator is a simple screening tool that estimates whether a person has a healthy body weight for their height. Used by healthcare professionals worldwide, BMI is calculated by dividing your weight by your height squared. While not a diagnostic tool, BMI provides a quick and reliable indicator of potential weight-related health risks, including heart disease, diabetes, and joint problems. The World Health Organization (WHO) classifies BMI into categories: Underweight (<18.5), Normal Weight (18.5-24.9), Overweight (25-29.9), and Obese (≥30).

How Does It Work?

Our calculator uses the standard BMI formula. In metric units, BMI = weight(kg) / height(m)². In imperial units, BMI = weight(lbs) / height(in)² × 703. The result is then compared against WHO classification standards. Simply enter your height and weight, select your preferred unit system, and your BMI score and weight category appear instantly. For best results, measure your height without shoes and your weight in the morning before eating.

Formula

Metric: BMI = weight(kg) / height(m)²\nImperial: BMI = weight(lbs) / height(in)² × 703\n\nWHO Classification:\n• < 18.5 = Underweight\n• 18.5-24.9 = Normal Weight\n• 25-29.9 = Overweight\n• 30-34.9 = Obese Class I\n• 35-39.9 = Obese Class II\n• ≥ 40 = Obese Class III

Who Uses This Tool?

• Individuals monitoring their weight and health
• Fitness trainers assessing client baseline metrics
• Doctors and nurses performing quick health screenings
• Insurance companies evaluating health risk profiles
• Researchers conducting population health studies

Pro Tips

• BMI doesn't account for muscle mass — athletes may have high BMI but low body fat
• For a complete picture, combine BMI with our Body Fat Calculator
• BMI categories are the same for adult men and women, but children use age-specific percentiles
• The WHO recommends using BMI alongside waist circumference for better health risk assessment

Frequently Asked Questions about BMI Calculator

Is BMI an accurate measure of health?

BMI is a screening tool, not a diagnostic test. It doesn't measure body fat directly, nor does it account for muscle mass, bone density, or fat distribution. However, for most people, it provides a useful starting point for health discussions. Combine it with other measurements for a complete picture.

What is a healthy BMI?

A BMI between 18.5 and 24.9 is considered normal or healthy weight for adults. Below 18.5 is underweight, 25-29.9 is overweight, and 30 and above indicates obesity. These ranges apply to adults over 20 years old.

Why does my BMI matter?

Higher BMI is associated with increased risk of several health conditions, including type 2 diabetes, cardiovascular disease, hypertension, certain cancers, and joint problems. Maintaining a healthy BMI through balanced diet and regular exercise reduces these risks.

Can BMI be wrong for athletes?

Yes. Muscle is denser than fat, so very muscular individuals may have a high BMI while having low body fat. For athletes, body fat percentage or waist-to-height ratio are often better indicators of health.

Free online BMI Calculator — no signup, 100% client-side processing. All data stays in your browser.