Gas Mileage Calculator
0 MPG
How Fuel Efficiency Is Calculated
This calculator works backward from a trip you've actually driven to tell you how efficient your vehicle is. For miles-per-gallon, the formula is simply MPG = distance driven ÷ fuel consumed. Enter either two odometer readings (the calculator subtracts them for you) or a known distance, along with how much fuel it took to cover that distance, and the result is your real-world MPG for that tank or trip. The metric equivalent, liters per 100 kilometers, is calculated the opposite way — L/100km = (fuel used in liters ÷ distance in km) × 100 — which is why a lower L/100km number means better efficiency, unlike MPG where higher is better.
US Gallons vs. UK (Imperial) Gallons
A US gallon (3.785 liters) is smaller than a UK imperial gallon (4.546 liters), so the same fuel economy expressed in "MPG" can look meaningfully different depending on which gallon is meant — a car rated at 40 UK MPG is only about 33 US MPG. This calculator shows all three common units (US MPG, UK MPG, and L/100km) side by side so you can compare against a spec sheet or another driver's numbers without doing the conversion by hand.
This Measures Efficiency, Not Trip Cost
This tool calculates how efficient your vehicle actually is based on fuel you've already burned. If instead you want to project what a future trip will cost using an assumed or known MPG figure, use the fuel cost calculator. And if you're tracking miles driven for a business tax deduction rather than fuel efficiency, the mileage calculator is the right tool instead.
Frequently Asked Questions
How do I calculate my car's gas mileage manually?
Fill the tank, reset the trip odometer (or note the reading), drive normally, then refill and record how many gallons it took to fill up again along with the miles driven. Divide miles driven by gallons used to get MPG. This calculator does that division for you and also converts the result to UK MPG and L/100km.
Why is my calculated MPG different from my car's advertised EPA rating?
EPA window-sticker MPG is measured under standardized lab conditions. Real-world MPG calculated from your own fill-ups reflects your actual driving style, terrain, weather, traffic, and how full you actually filled the tank each time, so some variance from the sticker value is normal and expected.