Fuel Economy Calculator
Calculate your actual MPG and fuel efficiency from real fill-up data — then compare to your vehicle's EPA rating and see exactly what you're spending per mile.
Fill up your tank completely, reset your trip odometer to 0, drive until low on fuel, then fill up again and enter those numbers below.
Optional — for cost calculations.
Compare your actual vs. rated fuel economy.
How to Accurately Measure Your MPG
The most accurate way to calculate fuel economy is the brim-to-brim method:
- Fill your tank completely until the pump clicks off automatically
- Reset your trip odometer to zero (or note your total odometer reading)
- Drive normally until your tank is low — the more miles the better
- Fill the tank completely again at the same station, using the same pump type
- Enter the miles driven and gallons added above
A single fill-up gives you a reasonable estimate, but averaging over 3–5 tanks gives a much more accurate picture of your real-world fuel economy.
Why Your Actual MPG Differs from EPA Ratings
The EPA tests are conducted in a controlled laboratory environment. Real-world MPG is typically 10–20% lower because of:
- Driving style — Aggressive acceleration and braking is the biggest factor
- Speed — Aerodynamic drag increases exponentially above 55 mph
- Temperature — Cold weather reduces MPG by 15–25% for conventional vehicles (more for EVs)
- AC use — Air conditioning can reduce MPG by 5–25% in stop-and-go traffic
- Terrain — Hills and mountains reduce efficiency significantly
- Cargo weight — Every 100 lbs reduces MPG by approximately 1%
MPG vs. L/100km: Which Is Better?
Both measure the same thing from different angles:
- MPG — Miles driven per gallon consumed. Higher = better.
- L/100km — Liters of fuel to travel 100 km. Lower = better.
L/100km is more intuitive for comparing fuel savings because it's directly proportional to fuel consumed — unlike MPG, where the efficiency gains are not linear.
Frequently Asked Questions
My actual MPG is much lower than EPA. What's wrong?
Start with tire pressure (under-inflation is common and impactful), air filter cleanliness, and driving habits. A tuned-up engine and steady highway driving should get you close to EPA ratings.
How do I find EPA MPG for my specific vehicle?
Visit fueleconomy.gov and search by year, make, and model. You can also find the Monroney sticker (window sticker) label for your specific trim level.
