BMI Calculator

Calculate BMI (Body Mass Index) from height and weight.

Input

Output

Examples

Example 1

70 175

Example 2

85 1.80

Example 3

60 165

Understanding BMI Calculation

BMI (Body Mass Index) is calculated as weight in kilograms divided by height in meters squared (BMI = kg/m²). For example, a person weighing 70kg at 1.75m tall has BMI = 70/(1.75²) = 22.9. This simple ratio provides a general indicator of body composition.

The WHO classifies BMI into categories: Underweight (<18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obese (≥30, with subcategories I, II, III). These thresholds correlate with health risks but don't account for individual factors like muscle mass or bone density.

BMI has limitations: It doesn't distinguish between muscle and fat, doesn't account for fat distribution (visceral vs subcutaneous), and uses different thresholds for different ethnicities. Athletes may have 'overweight' BMI due to muscle, while sedentary individuals with normal BMI may have unhealthy body fat percentages.

BMI in Health and Fitness Applications

Healthcare providers use BMI as a screening tool for weight-related health risks. While not diagnostic alone, BMI correlates with risks of diabetes, heart disease, and hypertension. It provides a quick, non-invasive metric for population health studies and individual assessments.

Fitness applications track BMI over time to visualize weight loss or muscle gain progress. Combining BMI with other metrics (body fat percentage, waist circumference, strength measurements) provides a complete picture. BMI alone can be misleading for fitness goals focused on muscle gain.

Insurance companies may use BMI for premium calculations, considering higher BMI a risk factor. This is controversial as BMI doesn't account for individual health variations. Some insurers now incorporate additional health metrics to create more fair and accurate assessments.

Implementing BMI Calculators

Support multiple unit systems: Metric (kg, cm/m) and Imperial (lbs, inches/feet). Convert Imperial to metric internally: weight(kg) = lbs × 0.453592, height(m) = inches × 0.0254. Display results in user's preferred units for convenience.

Validate input ranges: Reject unrealistic values (height <50cm or >300cm, weight <10kg or >500kg) that indicate data entry errors. Provide helpful error messages guiding users to correct format (e.g., 'Enter height in cm, not mm').

Show BMI category with context: Don't just display a number—explain what it means. 'BMI: 24.5 (Normal weight)' is more useful than '24.5' alone. Include health recommendations or warnings for extreme categories, but note BMI limitations.

Calculate related metrics: Ideal weight range based on height and normal BMI category (18.5-24.9), weight needed to reach target BMI, or BMI-for-age percentiles for children. These actionable insights are more valuable than raw BMI numbers.

BMI Alternatives and Enhancements

Waist-to-height ratio (WHtR) better predicts health risks by accounting for abdominal fat distribution. A ratio >0.5 indicates increased risk regardless of BMI. Combining BMI with WHtR provides more comprehensive health assessment.

Body fat percentage directly measures composition, distinguishing fat from lean mass. Methods include bioelectrical impedance, DEXA scans, or skinfold calipers. While more accurate than BMI, these require specialized equipment or calculations.

Ethnic-specific BMI thresholds address population differences: Asian populations have higher health risks at lower BMI values. WHO recommends BMI ≥23 as overweight for Asian adults versus ≥25 for other populations. Calculators should support ethnicity-specific thresholds.

BMI-for-age percentiles assess children and teens, comparing BMI to peers of same age and sex. Growing children can't use adult BMI categories—percentile charts account for developmental changes. Pediatric BMI calculators require age input for accurate assessment.

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BMI Calculator - Body Mass Index Calculator

Calculate BMI (Body Mass Index) from height and weight.

Calculate Body Mass Index (BMI) to assess body weight relative to height. Perfect for health tracking, fitness planning, medical assessments, and weight management. Provides BMI value with WHO classification (underweight, normal, overweight, obese) and health recommendations.

Keywords

#bmi calculator#body mass index#health calculator#weight calculator#fitness tool#bmi

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BMI Calculator

Calculate BMI (Body Mass Index) from height and weight.

Input

Output

Examples

Example 1

70 175

Example 2

85 1.80

Example 3

60 165