function calculateMPG() {
var start = parseFloat(document.getElementById('startOdometer').value);
var end = parseFloat(document.getElementById('endOdometer').value);
var gallons = parseFloat(document.getElementById('gallonsUsed').value);
var price = parseFloat(document.getElementById('fuelPrice').value);
if (isNaN(start) || isNaN(end) || isNaN(gallons) || gallons <= 0 || end 0) {
var totalCost = gallons * price;
var costPerMile = totalCost / totalMiles;
document.getElementById('resTotalCost').innerText = "$" + totalCost.toFixed(2);
document.getElementById('resCostPerMile').innerText = "$" + costPerMile.toFixed(2);
document.getElementById('costSection').style.display = 'block';
} else {
document.getElementById('costSection').style.display = 'none';
}
document.getElementById('mpgResults').style.display = 'block';
}
How Do You Calculate Your Miles Per Gallon?
Understanding your vehicle's fuel efficiency is essential for budgeting and monitoring your car's mechanical health. Miles per gallon (MPG) represents how many miles your vehicle can travel on a single gallon of fuel. A sudden drop in MPG often indicates that your vehicle needs maintenance, such as a tire pressure check or a new air filter.
The Step-by-Step Manual Calculation
While modern cars have trip computers that estimate fuel economy, manual calculation is the most accurate way to verify your real-world consumption. Follow these steps:
Fill your tank: Go to the gas station and fill your tank until the pump stops automatically.
Record your mileage: Write down your current odometer reading (this is your Starting Odometer).
Drive normally: Use your car as you usually would until you need to refuel (at least half a tank is recommended for accuracy).
Refill and Record: Go back to the pump. Record the Ending Odometer reading and look at the pump receipt to see exactly how many Gallons you added to make the tank full again.
The MPG Formula
The mathematical formula for fuel efficiency is simple:
Let's say you filled up your car and the odometer read 45,000 miles. A week later, you fill up again when the odometer reads 45,300 miles. The pump shows you added 10 gallons of gas.
Total Miles Driven: 45,300 – 45,000 = 300 miles.
Calculation: 300 miles / 10 gallons = 30 MPG.
What Factors Affect Your MPG?
Several variables can cause your fuel economy to fluctuate from week to week:
Driving Habits: Aggressive acceleration and heavy braking significantly reduce efficiency.
Tire Pressure: Under-inflated tires increase rolling resistance, forcing the engine to work harder.
Weight: Carrying unnecessary heavy items in the trunk or using a roof rack increases drag and fuel consumption.
Idling: If you spend a lot of time in gridlock or idling the engine, your MPG will plummet because you are burning fuel without moving.
Terrain: Driving in hilly areas or on unpaved roads requires more energy than flat highway cruising.
Why Use an MPG Calculator?
Using our MPG calculator allows you to track your fuel costs over time. By entering the price per gallon, you can see exactly how much each mile costs you to drive. This is incredibly helpful for long-distance trip planning and for business owners who need to track travel expenses for tax purposes.