MPG Calculator
Calculate fuel economy, annual costs, and CO₂ emissions
US average is approximately 12,000 miles/year
Enter Trip Data
Enter the distance driven and fuel used to calculate your vehicle's fuel economy.
How to Use the MPG Calculator
Select Your Unit System
Choose US (miles and US gallons), Imperial (miles and Imperial gallons, used in the UK), or Metric (kilometers and liters). This determines the units for your distance and fuel inputs, but all results are shown in all formats regardless of selection.
Enter Trip Data
Enter the total distance driven and the total fuel used for the trip. For the most accurate result, fill your tank completely, note the odometer, drive until the next fill-up, and use the distance driven and gallons pumped at the second fill-up. Also enter your local fuel price and annual driving distance for cost calculations.
Review Your Results
The hero result shows your MPG in US units, with Imperial MPG, km/L, and L/100km below. The efficiency bar chart compares your vehicle to benchmark averages. The cost breakdown shows per-mile cost, annual fuel expenditure, and annual gallons consumed. The environmental section shows annual CO₂ emissions.
Track and Export
Click 'Export CSV' to download your results for tracking fuel economy over time. Compare fill-ups to identify trends — consistent tracking can reveal maintenance issues early. Click 'Print' for a hard copy of your results.
Frequently Asked Questions
How do I accurately calculate my car's MPG?
The most accurate method is the tank-to-tank calculation. Fill your fuel tank completely at the pump, then reset your trip odometer (or note the current odometer reading). Drive normally until you need to refuel. At the next fill-up, fill the tank completely again and note exactly how many gallons the pump shows. Divide the trip distance by the gallons pumped: MPG = Trip miles ÷ Gallons pumped. For even better accuracy, repeat this over 3-5 fill-ups and average the results. This smooths out variations from different driving conditions, routes, and temperatures. Avoid using the fuel gauge or trip computer — they are less accurate than pump measurements.
What is the difference between US MPG and Imperial MPG?
US MPG uses the US gallon (3.785 liters) while Imperial MPG uses the Imperial gallon (4.546 liters). Since the Imperial gallon is about 20% larger, the same vehicle will show approximately 20% higher MPG in Imperial units. A car that gets 25 US MPG gets about 30 Imperial MPG. The UK and some other Commonwealth countries historically used Imperial gallons, while the US uses its own gallon. When comparing fuel economy numbers from different countries, always check which gallon standard is being used. The metric system avoids this confusion by using liters — km/L or L/100km have only one standard worldwide.
What is a good MPG for a car?
The 2024 US fleet average for all new cars and light trucks combined is approximately 25.4 MPG. A car achieving 30+ MPG is considered good by US standards. Hybrids typically achieve 45-55 MPG, and plug-in hybrids can exceed 100 MPGe (miles per gallon equivalent) when running on electricity. For sedans, 30-35 MPG is above average. For SUVs, 25-30 MPG is good. For trucks, 20-25 MPG is respectable. The most fuel-efficient non-plug-in cars on the market achieve 55-60 MPG. Context matters — a truck getting 22 MPG is performing well for its class even though a sedan at 22 MPG would be below average.
Why does my actual MPG differ from the EPA rating?
EPA fuel economy numbers are measured under standardized laboratory conditions using prescribed driving cycles, not on real roads. Several factors cause real-world MPG to differ: aggressive acceleration and braking (can reduce MPG by 15-30%), highway speeds above 50 mph (each 5 mph above 50 costs roughly 2-4% in fuel economy due to aerodynamic drag), cold weather (winter fuel blends have less energy per gallon, cold engines are less efficient, and tire rolling resistance increases), short trips (engines run less efficiently when cold), mountainous terrain, heavy loads, underinflated tires, and accessory use (air conditioning can reduce MPG by 3-5%). Gentle driving, proper tire inflation, and highway cruising typically yield MPG close to or above the EPA highway rating.
How do I convert MPG to L/100km?
The conversion formula is: L/100km = 235.215 ÷ MPG (US). For example, 30 US MPG = 235.215 ÷ 30 = 7.84 L/100km. For Imperial MPG: L/100km = 282.481 ÷ MPG (Imperial). The inverse relationship means that lower L/100km values indicate better fuel efficiency (opposite of MPG where higher is better). European fuel economy labels use L/100km as the standard. Approximate equivalents for reference: 20 MPG ≈ 11.8 L/100km, 25 MPG ≈ 9.4 L/100km, 30 MPG ≈ 7.8 L/100km, 35 MPG ≈ 6.7 L/100km, 40 MPG ≈ 5.9 L/100km, 50 MPG ≈ 4.7 L/100km.
Does driving slower always save fuel?
Yes, but with diminishing returns below about 35-40 mph. Fuel consumption has two main components: engine friction (dominant at low speeds) and aerodynamic drag (dominant at high speeds). The aerodynamic drag force increases with the square of speed, so doubling speed quadruples drag. Most vehicles hit their peak fuel efficiency between 35-55 mph. Above 50 mph, every additional 5 mph costs roughly 2-4% in fuel economy. At 75 mph, a car typically uses 20-30% more fuel than at 55 mph for the same distance. However, driving extremely slowly (under 25 mph) in high gears is also inefficient because the engine operates outside its optimal efficiency range. The sweet spot for most vehicles is steady cruising at 45-55 mph in the highest gear — which is why highway MPG ratings are often tested at 48 mph average speed.