How much gas idling uses
fueleconomy.gov puts idling at "a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner (AC) use." A small four-cylinder with the AC off sits near the low end. A bigger engine, or any engine running the AC on a hot day, sits near the top.
You'll find higher and lower numbers online, mostly from fleet software companies and forum posts, ranging from about 0.15 to 0.7 gallons an hour for passenger vehicles. That spread is real: engine size, outside temperature and accessories all change it. The calculator uses fueleconomy.gov's range because it's the official figure, but you can type any rate you like.
How much gas does idling for 15 minutes use?
Fifteen minutes is a quarter of an hour, so it uses a quarter of the hourly rate: about 0.06 to 0.13 gallons. Twenty minutes uses about 0.08 to 0.17 gallons.
How many miles is an hour of idling?
Multiply the gallons by your MPG. At 25 MPG, the quarter to half gallon an idling engine burns in an hour would have taken you about 6 to 12.5 miles down the road. In a 35 MPG car it's about 9 to 17.5 miles.
What idling costs: a worked example
- Fuel a day: 10 minutes ÷ 60 × 0.5 gallons an hour = 0.083 gallons
- Fuel a year: 0.083 × 250 days = 20.8 gallons
- Cost a year: 20.8 gallons × an example $3.50 = $72.92
- Same fuel in a 25 MPG car: 20.8 × 25 = about 521 miles of driving
At the low end of the range, 0.25 gallons an hour, the same habit costs about $36.46 a year. Either way, it's money spent going nowhere. If most of your idling happens in traffic on the way to work, the commute cost calculator shows what the whole trip costs.
When to turn the engine off
Two U.S. Department of Energy sources answer this, and they use different cutoffs for good reasons.
- On fuel alone, about 10 seconds. The Department of Energy's Vehicle Technologies Office, citing Argonne National Laboratory research, says "idling an engine for as little as 10 seconds will use more fuel than stopping and restarting the vehicle."
- Counting wear, about 1 minute. fueleconomy.gov says it only takes about 10 seconds' worth of fuel to restart, suggests limiting starts to about 10 a day unless the car has a start-stop system, and says that within that limit "any shutdown longer than 1 minute will save money."
So for a quick pause at a light, keep the engine running. If you're parked and waiting, in a pickup line or outside a store, turn it off. Argonne's Linda Gaines adds that for typical drivers making 10 or fewer starts a day, the starter motor "is unlikely to need to be replaced during the vehicle's life."
Does idle stop actually save gas?
Built-in start-stop systems shut the engine off at lights for you. Consumer Reports points to SAE International tests in which vehicles with the feature used 7 to 26 percent less fuel. The savings are biggest in stop-and-go city driving.
Do you need to warm up the engine?
Not for long. fueleconomy.gov says most manufacturers recommend driving off gently after about 30 seconds, and that "the engine will warm up faster being driven." Long warm-ups are just idling with a different name. Running the AC while you wait does the same thing, and our page on AC and gas covers that cost.
Cedrick Reese built this calculator for the small, daily idling that never shows up on a fuel receipt: the school pickup line, the drive-through, the five minutes waiting outside with the engine running. The idle rate, restart guidance and warm-up advice all come from fueleconomy.gov and the Department of Energy's Vehicle Technologies Office, with the Argonne research linked so you can read it yourself. The math is minutes × gallons per hour × days × price, and the worked example above is the check. The page is reviewed when those sources update, and the gas price shown is only an example.
Idling questions
How much gas does idling use per hour?
fueleconomy.gov says idling can use a quarter to a half gallon of fuel per hour, depending on engine size and AC use. Smaller engines with the AC off use the least.
How much gas does idling for 15 minutes use?
About 0.06 to 0.13 gallons, which is a quarter of the hourly rate of a quarter to a half gallon. At an example price of $3.50 a gallon, that's roughly 22 to 44 cents.
Is it better to idle or turn off the engine?
If you'll be stopped for more than a minute, turn it off. The Department of Energy says idling for as little as 10 seconds uses more fuel than restarting, and fueleconomy.gov says any shutdown longer than 1 minute saves money once starter wear is counted, as long as you stay around 10 starts a day.
Is idling for 20 minutes bad?
It wastes fuel and gets you nowhere. Twenty minutes of idling uses about 0.08 to 0.17 gallons. fueleconomy.gov notes that most manufacturers recommend driving off gently after about 30 seconds instead of warming up the engine by idling.
How many miles is 1 hour of idle?
Multiply the quarter to half gallon an hour of idling burns by your MPG. At 25 MPG, an hour of idling uses the fuel for about 6 to 12.5 miles of driving.
More fuel tools
To see what your daily drive costs, use the commute cost calculator. For the cost of any single trip, use the fuel cost calculator.
Idling is one of several small habits that add up. How to save money on gas shows what each one is worth at your own driving.
Sources
Last reviewed: October 4, 2026.
- fueleconomy.gov, Driving More Efficiently
- U.S. Department of Energy, FOTW #1239: Idling an engine for as little as 10 seconds will use more fuel than stopping and restarting
- Argonne National Laboratory, Ask a scientist: When is it more efficient to turn off my car instead of idling?
- fueleconomy.gov, Fuel Economy in Cold Weather
- Consumer Reports, Expert Fuel-Saving Tips