How much gas does a car use idling for an hour? According to research from Argonne National Laboratory for the U.S. Department of Energy, a typical passenger car burns about 0.2 to 0.5 gallons of fuel per hour while idling. Smaller engines sit at the low end, and larger V6 and V8 engines at the high end. Running the air conditioner or other accessories pushes consumption higher still.
Idling Fuel Use by Engine Size
Idle fuel consumption rises steadily with engine displacement, because a bigger engine has to burn more fuel just to keep turning over. As a rough guide:
| Vehicle / Engine | Approx. Fuel Use at Idle |
|---|---|
| Small car, 4-cylinder | 0.2–0.3 gal/hr |
| Midsize car or crossover, V6 | 0.3–0.4 gal/hr |
| Full-size truck or SUV, V8 | 0.5 gal/hr or more |
Using the A/C, heater blower, rear defroster, or heavy electrical accessories can noticeably raise these numbers. So can a cold engine that’s still warming up.
What an Hour of Idling Actually Costs
To estimate your cost, multiply your idle fuel use by your local gas price. At $3.50 per gallon, a car burning 0.3 gallons per hour costs about $1.05 per hour to idle. A V8 truck burning 0.5 gallons per hour costs about $1.75. That may not sound like much, but daily idling adds up. Twenty minutes a day in a pickup line or drive-through can waste several gallons a month while going nowhere.
Is It Better to Turn the Engine Off?
Usually, yes. Argonne’s testing found that idling for more than about 10 seconds uses more fuel, and produces more CO2, than turning the engine off and restarting it. That’s why many newer cars have automatic start-stop systems. The exception is in traffic, where you need to keep moving, and in very cold or hot weather, where you may need the engine running for heat or cooling.
Is Long Idling Bad for Your Engine?
Extended idling isn’t just wasteful. A modern engine doesn’t need a long warm-up, and idling for long periods can let the engine run below its ideal temperature, which may lead to incomplete combustion and fuel or carbon deposits over time. Keeping fuel injectors clean helps the engine run efficiently, and our guide on how to clean fuel injectors covers that. If your idle feels rough or shaky, that’s a separate issue worth diagnosing. See why your car is shaking for common causes.
Watch your temperature gauge, too. Idling in hot weather with the A/C running puts extra load on the cooling system. If the needle climbs, read what to do when your car overheats.
Conclusion
So, how much gas does a car use idling for an hour? Most passenger cars burn about 0.2 to 0.5 gallons, with small 4-cylinders at the low end and V8 trucks at the high end, and more with the A/C on. Since restarting uses about the same fuel as 10 seconds of idling, turning the engine off during longer waits saves gas and money. Good habits like this belong on your car maintenance checklist, too.
Frequently Asked Questions
How much gas does idling for 10 minutes use?
For a car burning 0.3 gallons per hour at idle, 10 minutes uses about 0.05 gallons. A V8 truck at 0.5 gallons per hour would use roughly 0.08 gallons.
Does running the A/C while idling use more gas?
Yes. The A/C compressor puts extra load on the engine, which raises idle fuel use, sometimes noticeably on hot days.
Does restarting the engine waste more gas than idling?
No. Argonne National Laboratory found that idling for more than about 10 seconds uses more fuel than shutting the engine off and restarting it.
How long can a car idle on a full tank?
In theory, a car burning 0.3 gallons per hour with a 14-gallon tank could idle for well over a day. But extended idling wastes fuel, risks overheating in hot weather, and is unsafe in enclosed spaces due to carbon monoxide.
