How do I find out the mpg of my car?

Knowing your car’s fuel economy, or miles per gallon (MPG), can help you budget for fuel costs, compare the efficiency of different models, and evaluate upgrades that can improve efficiency. Calculating your car’s real-world MPG is easy to do yourself.

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What equipment do I need?

The only equipment you need is:

Your car

A full tank of gas
A pen and paper (or MPG tracking app) to record data

Newer vehicles may display a real-time MPG estimate on the dashboard. But to get a true MPG figure, you’ll need to calculate it yourself based on actual fuel consumption.

How do I calculate MPG?

The basic formula for calculating MPG is:

MPG = Miles driven / Gallons of fuel used

For example, if you drove 300 miles before refueling 10 gallons, the calculation would be:

MPG = 300 miles / 10 gallons = 30 MPG

To test your car’s MPG, follow this simple procedure:

Fill up your gas tank to the very top at a gas station and note the current odometer reading.

After at least 5-10 miles of driving, fill up the tank again, taking care to fill up to the very top. Note the new odometer reading and how many gallons it took to refill.
Subtract the first odometer reading from the second to get the total miles driven.
Divide the miles driven by the gallons added during the second fill-up.

Let’s say the first odometer reading was 125,000 miles. After driving 315 miles, you added 12.8 gallons at the pump. Here’s the MPG calculation:

Total miles driven: 125,315 – 125,000 = 315 miles
Gallons added: 12.8
MPG = 315 / 12.8 = 24.6 MPG

This procedure will give you your actual MPG over that tank of gas. For accuracy, repeat this every few tank refills and average the MPG calculations.

What affects MPG?

Many factors can influence fuel efficiency and cause MPG fluctuations:

Vehicle weight – Heavier loads reduce MPG.
Tire inflation – Underinflated tires increase rolling resistance.

Driving style – Aggressive acceleration and braking lowers MPG.
Speed – Higher speeds, especially over 50 mph, decrease MPG.
Maintenance – Issues like a faulty oxygen sensor, clogged air filter, and dirty spark plugs can lower MPG.

Fuel type – Premium grades with higher octane provide no MPG benefit unless required by the engine.
Cold weather – MPG is typically lower in winter temperatures.
Air conditioning – Running the A/C compressor increases load on the engine.

Driving conservatively, keeping your vehicle well-maintained, and using the recommended grade of fuel will help optimize MPG.

How can I improve my car’s MPG?

If your calculated MPG is lower than expected, there are steps you can take to improve it:

Inflate tires to the pressure listed inside the driver’s door or owner’s manual, not the sidewall.

Use the recommended grade of motor oil and keep up with oil changes.
Replace dirty air filters and old spark plugs.
Use a fuel additive like Techron regularly to clean fuel injectors.

Lighten your load by removing unnecessary cargo.
Avoid aggressive driving habits like speeding, rapid acceleration and hard braking.
Reduce highway speeds. Driving above 50 mph rapidly decreases MPG.

Limit idling to warm up the engine for no more than 30 seconds.
Install a digital MPG display like ScanGauge to monitor MPG in real-time.

Upgrading to a more efficient vehicle is also an option if poor MPG persists. Compare the EPA ratings among similar model years when shopping for a new or used car.

How accurate is the EPA MPG estimate?

The Environmental Protection Agency (EPA) conducts extensive testing to estimate the fuel economy of vehicles sold in the US. However, most drivers experience lower MPG compared to the published EPA figures. There are a few reasons for this:

EPA tests are conducted in controlled lab conditions with professional drivers, not real-world conditions.
The tests use specific speeds and acceleration rates that are more efficient than typical driving habits.

Ambient weather is regulated during testing. Real-world heat, cold, rain, snow and wind lower MPG.
EPA only tests city and highway cycles. Combined MPG is an estimate.

While EPA estimates can be useful for comparison shopping, your real-world MPG will likely be 10-20% lower based on driving conditions and habits. Measuring MPG yourself provides a more accurate picture of your car’s efficiency.

How can I track and record MPG?

Consistently tracking your fuel economy helps identify trends and areas for improvement. Here are some methods to record MPG data:

MPG log – Document odometer readings, gallons added and calculated MPG in a notebook or spreadsheet after each fill-up.
Fuelly – This popular free app lets you input data to generate MPG performance reports.

ScanGauge – Displays real-time MPG, average MPG and MPG history right on your dashboard.
Dash computer – Many late model vehicles have a trip computer that estimates MPG. View average MPG displays.
OBD scanner – Bluetooth adapters connect to your car’s OBD-II port to capture MPG data.

Reviewing MPG logs regularly can reveal the effects of different driving scenarios, maintenance issues or modifications. Any sudden MPG drops are easier to identify so you can address problems promptly.

How does my MPG compare?

The average MPG of passenger vehicles in the US has steadily increased over the past decades due to fuel economy regulations and more efficient engine technology. Here are the key trends:

In 1980, average MPG was 20.

This rose to 28 MPG in 2008 as fuel prices spiked.
The latest data shows average MPG is around 29 for 2019 passenger cars.
Hybrids and electric cars are lowering fleet averages with MPG ratings between 40 to over 100 MPGe.

The average pickup truck MPG is 21, while large SUVs average 18 MPG.

Your individual MPG will depend on your car’s size, performance, transmission, fuel type and driving patterns. Comparing to the averages for your vehicle class will give you an idea of your efficiency. If your MPG is significantly lower than competitors, look into ways to improve it.

Average MPG by Vehicle Type

Vehicle Type	Average MPG
Small sedan	31
Midsize sedan	28
Large sedan	25
Small SUV	26
Midsize SUV	22
Large SUV	18
Pickup truck	21
Minicompact	33
Subcompact	32
Compact	30
Hybrid	50
Electric	100+ MPGe

Should I use premium fuel to boost MPG?

Drivers often wonder if filling up with premium gasoline will improve fuel economy. The answer depends on your vehicle:

For most cars designed for regular fuel, premium provides no MPG benefit and is a waste of money.
Premium fuel can raise MPG marginally in some turbocharged engines.
Using premium in an engine requiring lower octane could actually reduce efficiency.

Cars requiring premium fuel see significant MPG drops from using regular gasoline.

Always consult your owner’s manual on the recommended fuel grade. Unless specified as requiring premium, opting for regular gasoline will not sacrifice MPG. The higher cost per gallon negates any minor efficiency advantage.

How long can I drive on empty to maximize MPG?

Trying to squeeze out every last mile before your next fill-up is not advisable. Here are the downsides:

Running on fumes risks stalling out on the road if you miscalculate range.
Fuel pumps can overheat when drawing fuel from a near-empty tank.
Sediment at the bottom of the tank can get sucked into fuel lines.

You may have to slow down as the tank gets low, reducing MPG.
Partial tank refills make accurately tracking MPG more difficult.

The optimal strategy is refilling at 1/4 tank remaining. This minimizes risks, keeps MPG tests consistent, and allows for some margin of error in range. The minor MPG gain from carrying less fuel is not worth potential headaches.

Does fuel economy decrease over time?

Fuel efficiency tends to gradually decline as a car ages and accumulates mileage for a few reasons:

Engine seals and moving components wear down increasing friction.
Oxygen sensors get coated with residue reducing effectiveness.

Oil becomes sludgy and fails to lubricate efficiently.
Carbon buildup inside the engine affects airflow and combustion.
Transmission shift points deteriorate.

Misfiring spark plugs waste fuel.

Proper maintenance can help minimize MPG reductions. But even well-maintained engines lose a bit of their peak efficiency over decades and hundreds of thousands of miles. How drastically MPG drops depends on the make and model. Testing your MPG at least yearly provides insight into how age affects your car’s fuel economy.

Conclusion

Knowing the true MPG of your vehicle enables realistic fuel budgeting and can motivate efficiency improvements. Avoid relying only on the EPA estimate or dashboard display for accuracy. While a precise tanks-full calculation requires some diligence, the insight gained from regularly tracking your fuel economy in real-world conditions is extremely beneficial as a car owner.