Calculating your vehicle's fuel efficiency is a critical skill for managing travel budgets and monitoring vehicle health. The most accurate way to calculate mileage is by using the "full tank" method.
Fill your tank: Fill the tank until the pump clicks off. Record your current mileage (Starting Odometer).
Drive normally: Go about your daily routine until the tank is at least half empty.
Refill and record: Go back to the gas station. Fill the tank again and record two things: the new mileage (Ending Odometer) and exactly how many gallons it took to refill the tank.
Subtract: Subtract the starting mileage from the ending mileage to find the distance driven.
Divide: Divide the distance by the gallons used.
Practical Example
Suppose you start with an odometer reading of 12,000 miles. You drive for a week and refill the tank. Your new reading is 12,300 miles, and the pump says you added 10 gallons of gas. The price of gas was $3.50 per gallon.
Distance: 12,300 – 12,000 = 300 miles
MPG: 300 / 10 = 30 MPG
Total Cost: 10 * $3.50 = $35.00
Cost Per Mile: $35.00 / 300 = $0.11 per mile
Why Monitoring Mileage Matters
A sudden drop in fuel efficiency can be an early warning sign of mechanical issues, such as low tire pressure, a clogged air filter, or failing oxygen sensors. By keeping a log of your MPG, you can save money on both fuel and long-term maintenance costs.
function calculateMileage() {
var start = parseFloat(document.getElementById('startOdo').value);
var end = parseFloat(document.getElementById('endOdo').value);
var fuel = parseFloat(document.getElementById('fuelQty').value);
var price = parseFloat(document.getElementById('fuelPrice').value);
if (isNaN(start) || isNaN(end) || isNaN(fuel) || fuel <= 0) {
alert("Please enter valid numbers for Odometer readings and Fuel quantity.");
return;
}
var distance = end – start;
if (distance <= 0) {
alert("Ending odometer must be higher than starting odometer.");
return;
}
var mpg = distance / fuel;
var totalCost = 0;
var costPerMile = 0;
if (!isNaN(price)) {
totalCost = fuel * price;
costPerMile = totalCost / distance;
}
document.getElementById('resDistance').innerText = distance.toLocaleString(undefined, {minimumFractionDigits: 1, maximumFractionDigits: 1});
document.getElementById('resMPG').innerText = mpg.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
if (!isNaN(price)) {
document.getElementById('resTotalCost').innerText = '$' + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resCostMile').innerText = '$' + costPerMile.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
} else {
document.getElementById('resTotalCost').innerText = 'N/A';
document.getElementById('resCostMile').innerText = 'N/A';
}
document.getElementById('mileageResult').style.display = 'block';
}