Converting miles per gallon to kilometer per liter in JavaScript

Converting miles per gallon (MPG) to kilometers per liter (km/L) is a common unit conversion in JavaScript applications dealing with fuel efficiency across different measurement systems.

Understanding the Conversion

To convert MPG to km/L, we need two conversion factors:

• 1 mile = 1.609344 kilometers
• 1 gallon = 4.54609188 liters (Imperial gallon)

The conversion formula is: km/L = MPG × (1.609344 ÷ 4.54609188)

Example Implementation

const num = 25;
const converter = (mpg) => {
    let LITRES_PER_GALLON = 4.54609188;
    let KILOMETERS_PER_MILE = 1.609344;
    const ratio = KILOMETERS_PER_MILE / LITRES_PER_GALLON;
    return Math.round(100 * mpg * ratio) / 100;
};
console.log(converter(num));

8.85

Enhanced Version with Validation

Here's an improved version with input validation and better readability:

function mpgToKmL(mpg) {
    // Input validation
    if (typeof mpg !== 'number' || mpg <= 0) {
        throw new Error('Input must be a positive number');
    }
    
    const LITERS_PER_GALLON = 4.54609188;
    const KILOMETERS_PER_MILE = 1.609344;
    const conversionRatio = KILOMETERS_PER_MILE / LITERS_PER_GALLON;
    
    // Round to 2 decimal places
    return Math.round(mpg * conversionRatio * 100) / 100;
}

// Test with different values
console.log(`25 MPG = ${mpgToKmL(25)} km/L`);
console.log(`30 MPG = ${mpgToKmL(30)} km/L`);
console.log(`40 MPG = ${mpgToKmL(40)} km/L`);

25 MPG = 8.85 km/L
30 MPG = 10.62 km/L
40 MPG = 14.16 km/L

How It Works

The conversion process involves three steps:

1. Calculate the conversion ratio: 1.609344 ÷ 4.54609188 ? 0.354
2. Multiply the MPG value by this ratio
3. Round the result to 2 decimal places using Math.round()

US vs Imperial Gallons

Note that this example uses Imperial gallons (4.546 L). For US gallons (3.785 L), use this version:

function mpgToKmLUS(mpg) {
    const LITERS_PER_US_GALLON = 3.78541178;
    const KILOMETERS_PER_MILE = 1.609344;
    const conversionRatio = KILOMETERS_PER_MILE / LITERS_PER_US_GALLON;
    
    return Math.round(mpg * conversionRatio * 100) / 100;
}

console.log(`25 MPG (US) = ${mpgToKmLUS(25)} km/L`);

25 MPG (US) = 10.62 km/L

Conclusion

Converting MPG to km/L requires understanding the conversion ratios between miles/kilometers and gallons/liters. The key is applying the correct gallon measurement (Imperial vs US) for accurate results.