Quick answers
Your vehicle’s fuel economy, often called mileage, can be influenced by many factors. The EPA fuel economy estimates for new vehicles provide a standard way to compare vehicles when shopping for a new car or truck. For vehicles you already own, calculating your actual fuel economy can help you understand your vehicle’s performance and make informed decisions about maintenance and driving habits.
What influences fuel economy?
Some key factors that affect fuel economy include:
- Vehicle size and weight – Heavier vehicles require more energy to accelerate and move.
- Engine size and cylinders – More cylinders and larger displacement use more fuel.
- Fuel type – Diesel, hybrid, plug-in hybrid, and electric vehicles get better mileage than gasoline only.
- Transmission type – Manual transmissions often get better mileage than automatics.
- Driving habits – Aggressive acceleration and braking lowers MPG.
- Maintenance – Poor maintenance increases wear and lowers MPG.
- Tire inflation – Underinflated tires create more rolling resistance.
- Accessories like roof racks – These create aerodynamic drag.
How is EPA fuel economy calculated?
The EPA uses standardized test procedures to measure the fuel economy of new vehicles. The city and highway fuel economy ratings are based on driving cycles that simulate typical city and highway driving. Vehicles are tested in a controlled lab environment on a dynamometer under repeatable conditions.
This allows for an apples-to-apples comparison between vehicles, but your actual on-road mileage may vary. Real-world factors like weather, traffic, terrain and driving style impact the actual fuel economy you experience.
Calculating your actual fuel economy
To calculate your real-world fuel economy, you’ll need to track a few pieces of information:
- Gallons of fuel used – From fill-ups at the gas station
- Miles driven – From your odometer
Then calculate:
Miles Per Gallon (MPG) = Miles Driven / Gallons Used
For example, if you drove 340 miles before refueling 11 gallons:
340 Miles / 11 Gallons = 30.9 MPG
To get the best results, track your mileage over a longer period of time. This helps account for variations in driving conditions. Apps and vehicle trip computers can make mileage tracking easier.
MPG factors to consider
- Fuel type – Are you using regular or premium gasoline? Higher octane provides no fuel economy benefit unless specified by your owner’s manual.
- Fill-up amount – Don’t top off your tank, which can affect the gallon measurements.
- Resets – Set your trip odometer or app tracker to 0 at each fill-up.
- Records – Consistently log each fill-up to detect trends over time.
Improving your fuel economy
If your actual MPG is lower than expected, some common ways to improve it include:
Maintenance
- Check engine air filter and replace when dirty.
- Check tire inflation monthly and inflate to recommended PSI.
- Use recommended engine oil and keep changed on schedule.
- Get regular tune-ups and follow the maintenance schedule.
Driving Habits
- Avoid aggressive acceleration and braking which waste fuel.
- Observe speed limits and avoid excessive speeds which increase aerodynamic drag.
- Minimize idling and avoid running the engine when not driving.
- Reduce added weight by removing unnecessary cargo.
- Avoid prolonged engine warm-ups and drive moderately until reaching operating temperature.
Fuel Economy Features
Newer vehicles may offer features that can help maximize MPG:
- Cylinder deactivation – Shuts off cylinders when power demand is low.
- Start-stop system – Shuts off the engine when idling such as at stoplights.
- Eco mode – Adjusts throttle response and other factors to optimize economy.
- Low rolling resistance tires – Specifically designed to reduce drag.
Leveraging these features and driving conservatively can help optimize your mileage. But remember that published fuel economy ratings are tailored estimates. Your specific results will vary.
Comparing your MPG to EPA estimates
The EPA’s fuel economy guide provides estimated city, highway and combined ratings for all new light-duty vehicles. You can compare your calculated MPG to the EPA estimates to evaluate your vehicle’s performance.
Significant variances of 10-15% or more between your figures and the EPA estimates may indicate potential maintenance issues or driving habits that reduce economy.
However, keep in mind:
- EPA tests use laboratory-controlled settings and professional drivers.
- Ratings prioritize repeatable comparative testing over completely accurate real-world results.
- Your driving style, location and vehicle condition impact MPG.
- MPG usually decreases over time due to wear.
A perfect match between your MPG and the EPA estimates is unlikely. But large discrepancies merit further diagnosis and potential adjustments.
When to be concerned about low MPG
As a rule of thumb, the following MPG drops may indicate issues with your vehicle:
- 10% lower than EPA combined estimate
- 15% lower than EPA highway estimate
- 20% lower than EPA city estimate
These are general guidelines – your expected MPG will depend on your specific vehicle configuration and driving habits.
If your MPG is significantly lower than expected, possible causes can include:
Maintenance issues
- Dirty air filters or clogged fuel injectors
- Low tire pressures
- Used the wrong type of oil or coolant
- Worn spark plugs
Part failures
- Defective fuel pump, mass airflow sensor or oxygen sensor
- Catalytic converter needing replacement
- Transmission issues like worn clutch or torque converter lockup failure
Mechanical issues
- Dragging brakes
- Wheel misalignment
- Engine running too hot
- Leaking coolant, oil, or failed gaskets
When to be concerned about high MPG
It’s rare, but some vehicles achieve significantly better fuel economy than EPA estimates. This can occur due to:
- Focused eco driving techniques
- Favorable driving routes and conditions
- Detailed vehicle maintenance
- Aftermarket modifications and tuning to maximize economy
However, if your vehicle shows much higher than expected MPG, it could also indicate:
Inaccurate measurement
- Incorrect fuel tank capacity used to calculate
- Inaccurate odometer reading
- Topping off fuel tank skewing gallons used
Car computer issue
- Faulty mass air flow sensor providing incorrect readings
- Onboard computer software needing recalibration
Mechanical issue
- Wheel speed sensor malfunction
- Transmission slipping causing odometer errors
If you achieve extremely high MPG, double check your measurements for errors. Consult your owner’s manual for computer recalibration procedures. Persistently high MPG could signal a sensor malfunction to be diagnosed.
Using MPG to budget fuel costs
Your calculated MPG can provide useful insights into real-world fuel consumption and costs:
Project future fuel needs
Planning a long trip? Estimate gallons needed = Total miles / MPG
Ex: 300 mile trip / 30 MPG = 10 gallons needed
Compare vehicles when shopping
Calculate annual fuel use for different MPG vehicles:
Annual miles / MPG = Annual gallons used
Ex: 12,000 miles / 25 MPG = 480 gallons
Vs.
12,000 miles / 35 MPG = 343 gallons
Set fuel budgets
Track your mileage and MPG over one month. Use the figures to estimate future monthly and annual fuel costs at current prices.
Ex:
900 miles driven
30 MPG
So 30 gallons used
At $4 per gallon:
900 miles cost $120 that month
Projecting $120 x 12 months = $1,440/year
Apps and devices to monitor MPG
Dedicated apps, onboard computers, and plug-in devices can make it easier to monitor your fuel economy:
Apps
Popular fuel tracking apps include:
- Fuelly – Track fill-ups and mileage on your phone.
- GasBuddy – Crowd-sources local gas prices and integrates with Fuelly.
- MileIQ – Logs trips and mileage driven for expense reporting.
Vehicle trip computers
Your vehicle’s dashboard display provides real-time and average fuel economy readouts from sensors. Newer systems integrate with maps and provide eco-coaching.
OBD2 plug-ins
Devices that plug into the OBD2 port under the dash connect to your smartphone to provide sensor data like MPG, engine diagnostics, and performance metrics. Leading options include Automatic, Hum, and ScanGo.
Sample vehicle MPG comparison
To compare MPG between different vehicles, here is a table with some sample EPA estimates and real-world owner reported figures:
| Vehicle Make & Model | EPA Combined MPG | Owner Reported MPG |
|---|---|---|
| Toyota Camry 4-cyl | 32 MPG | 29 MPG |
| Ford F-150 Pickup V6 | 21 MPG | 18 MPG |
| Honda Civic Sedan | 36 MPG | 33 MPG |
| Tesla Model 3 EV | N/A | 110 MPGe |
This shows how real-world MPG is often lower than EPA estimates. All-electric vehicles like the Tesla Model 3 use the MPGe metric to allow comparison to gasoline MPG.
Conclusion
Calculating your real-world MPG allows you to better understand your vehicle’s fuel efficiency. Compare your figures to EPA estimates to gauge performance. Large variances may indicate maintenance issues or inefficient driving. Apps and onboard computers can provide helpful tracking. Use your vehicle’s demonstrated MPG to estimate fuel costs and make informed purchase comparisons when shopping for your next car or truck. Focus on regular maintenance and efficient driving techniques to maximize your mileage.
