Find your car's real-world fuel economy from miles driven and gallons used.
MPG stands for miles per gallon — it measures how far your car travels on a single gallon of fuel. The higher your MPG, the less you spend on gas. It's one of the most practical numbers to know about your vehicle, especially as gas prices fluctuate. Tracking your real-world MPG over time also tells you when something is off with your car before it becomes a bigger problem.
The formula is straightforward: divide the miles you drove between fill-ups by the gallons it took to refill the tank. If you drove 350 miles and used 11.5 gallons, your MPG is about 30.4. Do this regularly and you'll quickly notice if your fuel economy drops — which can signal low tire pressure, a dirty air filter, or a mechanical issue that needs attention.
Compact cars typically achieve 30–40 MPG in combined city/highway driving. Mid-size sedans land in the 25–35 MPG range. SUVs run 20–28 MPG depending on size and drivetrain. Full-size pickup trucks average 18–24 MPG. Hybrid vehicles often reach 45–60 MPG, and plug-in hybrids can exceed that in EV-only mode. Battery electric vehicles are rated in MPGe (miles per gallon equivalent), typically 90–130 MPGe.
These are averages. Your actual MPG depends on driving conditions, load, and how you drive. A compact car averaging 38 MPG on the highway might only return 28 MPG in stop-and-go city traffic.
Every new car sold in the US comes with an EPA fuel economy rating, but most drivers get 10–20% less in real-world use. The EPA tests are conducted in controlled lab conditions — no wind, no hills, no aggressive driving, and no air conditioning. Real life doesn't look like that.
The biggest MPG killers are air conditioning (can reduce efficiency by 5–25% in hot weather), highway speeds above 65 mph, cold weather (both the engine and battery in hybrids/EVs lose efficiency below 40°F), carrying heavy loads or towing, and under-inflated tires. Each of these compounds on the others.
Once you know your MPG, you can calculate exactly what any trip will cost in fuel. Divide your total distance by your MPG to get gallons needed, then multiply by the current gas price. A 500-mile trip in a 28 MPG vehicle at $3.60/gallon costs about $64. The same trip in a 20 MPG truck costs $90. Over a year of commuting, that gap adds up to hundreds or thousands of dollars.
If you're comparing two vehicles, you can estimate annual fuel savings by multiplying the difference in annual gallons by the gas price. A driver putting 15,000 miles/year on a 22 MPG truck versus a 32 MPG sedan uses about 682 gallons vs 469 gallons — a difference of 213 gallons, or roughly $745/year at $3.50/gallon.
The single biggest factor is driving speed. Fuel economy drops sharply above 60 mph — for every 5 mph you drive over 50, you effectively pay about 18 cents more per gallon. Smooth, anticipatory driving (coasting to stops rather than braking hard, gradual acceleration) also makes a significant difference.
On the maintenance side, keep tires inflated to the recommended PSI (check monthly — tires lose about 1 PSI per month naturally), replace air filters on schedule, and use the motor oil grade your manufacturer recommends. Properly maintained vehicles consistently outperform neglected ones on fuel economy by 5–15%.
If you've driven outside the US, you've seen fuel economy expressed as liters per 100 kilometers (L/100km). Unlike MPG where higher is better, with L/100km lower is better — it tells you how many liters of fuel you burn to cover 100 km. To convert: divide 235.21 by your MPG to get L/100km. A 30 MPG car equals about 7.8 L/100km.
This calculator computes fuel economy based on the distance and fuel values you enter. Results reflect the specific trip or fill-up recorded and may not represent your vehicle's average long-term fuel economy. Actual MPG varies with driving conditions, traffic, weather, and vehicle condition. This tool is for informational purposes only.