C program to Calculate Body Mass Index (BMI)

Body Mass Index (BMI) is a health metric used to assess whether a person has a healthy body weight relative to their height. In C programming, we can calculate BMI using a simple formula.

Syntax

BMI = weight / (height * height)

Where weight is in kilograms and height is in meters.

Example: BMI Calculator

This example demonstrates how to calculate BMI using a function −

#include <stdio.h>

// Function to calculate BMI
float calculateBMI(float weight, float height) {
    return weight / (height * height);
}

int main() {
    float weight = 60.0;  // weight in kg
    float height = 1.7;   // height in meters
    float bmi;
    
    bmi = calculateBMI(weight, height);
    
    printf("Weight: %.1f kg
", weight);
    printf("Height: %.1f m
", height);
    printf("BMI: %.2f
", bmi);
    
    // BMI categories
    if (bmi < 18.5) {
        printf("Category: Underweight
");
    } else if (bmi < 25.0) {
        printf("Category: Normal weight
");
    } else if (bmi < 30.0) {
        printf("Category: Overweight
");
    } else {
        printf("Category: Obese
");
    }
    
    return 0;
}

Weight: 60.0 kg
Height: 1.7 m
BMI: 20.76
Category: Normal weight

Example: Interactive BMI Calculator

This example takes user input for weight and height −

#include <stdio.h>

float calculateBMI(float weight, float height) {
    return weight / (height * height);
}

int main() {
    float weight, height, bmi;
    
    printf("Enter weight in kg: ");
    scanf("%f", &weight);
    
    printf("Enter height in meters: ");
    scanf("%f", &height);
    
    bmi = calculateBMI(weight, height);
    
    printf("\nYour BMI is: %.2f
", bmi);
    
    return 0;
}

BMI Categories

Key Points

• BMI is calculated as weight (kg) / height² (m²)
• Height must be in meters for accurate calculation
• BMI provides a general health indicator but doesn't account for muscle mass
• Always validate input to ensure positive values for weight and height

Conclusion

Calculating BMI in C is straightforward using the standard formula. The program can be enhanced to include BMI categories and input validation for better user experience.