Understanding your vehicle's fuel efficiency is crucial for budgeting and monitoring your car's health. Miles per gallon (MPG) is the standard metric used to determine how far a vehicle can travel on a single gallon of fuel.
The MPG Formula
The mathematical formula for fuel economy is straightforward:
MPG = Total Miles Driven / Gallons of Fuel Used
Step-by-Step Calculation Guide
Fill Your Tank: Fill your gas tank to the top and record your current odometer reading (Starting Miles).
Drive Normally: Drive your vehicle until the tank is at least half empty or until you need to refuel.
Refill and Record: Fill the tank again and record two things:
The new odometer reading (Ending Miles).
The exact number of gallons it took to refill the tank.
Do the Math: Subtract the Starting Miles from the Ending Miles to get your Trip Distance. Divide that distance by the number of gallons added.
A Practical Example
Imagine you fill your tank and your odometer reads 12,000 miles. You drive for a few days and go back to the station. Your odometer now reads 12,350 miles, and it takes 10 gallons to fill the tank back up.
Total Distance: 12,350 – 12,000 = 350 miles.
Fuel Used: 10 gallons.
Calculation: 350 / 10 = 35 MPG.
Why Should You Track MPG?
Tracking MPG helps you identify mechanical issues before they become expensive repairs. A sudden drop in fuel efficiency could indicate low tire pressure, a clogged air filter, or failing oxygen sensors. Additionally, it allows you to calculate the cost of road trips and choose the most efficient routes or driving habits.
function calculateMPG() {
var startOdo = document.getElementById("startOdometer").value;
var endOdo = document.getElementById("endOdometer").value;
var tripDist = document.getElementById("tripDistance").value;
var fuel = document.getElementById("fuelAdded").value;
var price = document.getElementById("pricePerGallon").value;
var totalMiles = 0;
var resultArea = document.getElementById("mpgResultArea");
var output = document.getElementById("mpgOutput");
var metrics = document.getElementById("additionalMetrics");
// Determine Miles Driven
if (tripDist && tripDist > 0) {
totalMiles = parseFloat(tripDist);
} else if (startOdo && endOdo) {
totalMiles = parseFloat(endOdo) – parseFloat(startOdo);
}
// Validations
if (totalMiles <= 0) {
alert("Please enter a valid distance. Ending odometer must be greater than starting odometer.");
return;
}
if (!fuel || fuel <= 0) {
alert("Please enter the amount of fuel added.");
return;
}
var mpg = totalMiles / parseFloat(fuel);
// Display Main Result
resultArea.style.display = "block";
output.innerHTML = mpg.toFixed(2) + " MPG";
// Calculate Additional Metrics
var metricsHTML = "Total Distance: " + totalMiles.toFixed(1) + " miles";
metricsHTML += "Fuel Consumed: " + parseFloat(fuel).toFixed(2) + " gallons";
if (price && price > 0) {
var totalCost = parseFloat(fuel) * parseFloat(price);
var costPerMile = totalCost / totalMiles;
metricsHTML += "Total Trip Cost: $" + totalCost.toFixed(2) + "";
metricsHTML += "Cost Per Mile: $" + costPerMile.toFixed(2) + "";
}
metrics.innerHTML = metricsHTML;
// Scroll to results smoothly
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}