MPG Calculator
Miles per gallon (MPG) is the standard measure of fuel efficiency used in the United States. Knowing your actual MPG is the first step in understanding your vehicle's fuel costs, planning road trips, and tracking whether your car's performance is declining over time. Calculating it requires just two pieces of information: the miles driven and the gallons of fuel consumed. In practice, the most accurate method is to fill your tank completely, note your odometer reading, drive normally, then fill up again completely and note how many gallons it took and how far you drove. Dividing miles by gallons gives your real-world MPG. This calculator also converts your MPG to litres per 100 kilometres (L/100km), the metric standard used outside the United States, and estimates your annual fuel cost based on your expected mileage and current gas price. The U.S. Energy Information Administration publishes weekly national average gas prices at eia.gov, which you can use for a realistic annual cost estimate.
Fuel economy: -- MPG (-- L/100km)
MPG to L/100km conversion table
| MPG (US) | L/100km | MPG (Imperial) |
|---|---|---|
| 20 MPG | 11.76 L/100km | 24.0 MPG (imp.) |
| 25 MPG | 9.41 L/100km | 30.0 MPG (imp.) |
| 30 MPG | 7.84 L/100km | 36.0 MPG (imp.) |
| 35 MPG | 6.72 L/100km | 42.0 MPG (imp.) |
| 40 MPG | 5.88 L/100km | 48.0 MPG (imp.) |
| 50 MPG | 4.70 L/100km | 60.0 MPG (imp.) |
Note: US gallon = 3.785 L; Imperial gallon = 4.546 L.
Improving your vehicle's fuel economy
The EPA and Department of Energy recommend maintaining proper tire inflation, replacing dirty air filters, using the recommended motor oil grade, and avoiding excessive idling. Driving at moderate highway speeds (55-65 mph) can improve fuel economy by 10-15% compared to driving at 75 mph or above.
MPG: frequently asked questions
How do I calculate my MPG?
Fill up your tank completely and reset your trip odometer (or note the current odometer reading). Drive as normal. When you next fill up, note the gallons required to refill the tank completely and the miles driven since the last fill-up. Divide miles driven by gallons used to get your MPG.
What is L/100km and how does it relate to MPG?
L/100km (litres per 100 kilometres) is the fuel efficiency standard used in Canada, Australia, the EU, and most countries outside the United States. Lower L/100km is better (uses less fuel). The conversion is: L/100km = 235.214 / MPG (US gallons). A car with 30 MPG uses approximately 7.84 L/100km.
Why is my actual MPG lower than the EPA rating?
EPA fuel economy estimates are generated under controlled laboratory conditions. Real-world driving involves factors that reduce efficiency: higher highway speeds, aggressive acceleration, air conditioning use, cold starts, hills and terrain, and vehicle load. Most drivers experience 10-20% lower fuel economy than the EPA estimate.
How does annual fuel cost get calculated?
Annual fuel cost = (annual miles / MPG) * price per gallon. For example, driving 12,000 miles per year at 30 MPG with gas at $3.50/gallon costs ($12,000 / 30) * $3.50 = 400 * $3.50 = $1,400 per year in fuel.
What is the average MPG for US drivers?
The U.S. Department of Transportation reports that the average fuel economy of light-duty vehicles sold in the US has been increasing steadily due to fuel economy standards. According to the EPA, new passenger vehicles averaged approximately 26-28 MPG combined in recent model years. Check the EPA's annual Fuel Economy Trends Report for the latest figure.
References
- U.S. Department of Energy. "Fuel Economy: Calculations and Reference." fueleconomy.gov
- U.S. EPA. "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends Report." epa.gov
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.