Global Fuel CalculatorHow much gas does the AC use?
A little, most of the time, and quite a lot in the wrong conditions. The compressor that cools your cabin is driven by the engine, so every minute it runs takes power that would otherwise move the car.
Why the AC uses fuel
In a conventional car the air conditioning compressor is driven by the engine, so it adds a load the engine has to carry by burning more fuel. In a hybrid or an electric car the power comes from the battery instead, so the cost shows up as fewer miles of range rather than extra fuel.
When it costs the most
The penalty is largest in very hot weather, on short stop-and-go trips, and while cooling a car that has been baking in the sun, because the system works hardest while the engine covers little distance. US government fuel-economy testers have reported that in extreme heat the AC can cut a conventional car's economy by roughly a quarter. On a mild day at a steady speed the effect is much smaller.
AC or open windows?
At low speed, open windows are generally the cheaper way to stay cool. At motorway speed, open windows add drag and many tests suggest the AC is the better choice. Your car and your speed shift the balance, so the next section shows how to check.
Measure it yourself
- Pick a repeatable route and fill to the same cut-off each time.
- Drive one tank with the AC on and a similar one with it off, in similar weather.
- Enter the distance and fuel for each tank into the fuel consumption calculator and compare the L/100km or MPG figures.
- Multiply the difference by the fuel price to see what the AC really costs you.
Ways to cut the cost
- Park in the shade and open the windows for a minute before switching the AC on.
- Use the recirculation setting once the cabin is cool.
- Choose a sensible temperature; a lower setting makes the system work harder.
Common questions
Does turning the AC off save gas?
Yes, it removes the compressor's load, so consumption drops. How much you save depends mostly on how hot it is and how much of your driving is short and stop-and-go.
Does a higher AC temperature use less fuel?
Usually. A less demanding setting means the compressor runs less often, so it takes less power from the engine.
How can I work out what the AC costs on a long trip?
Measure your economy with the AC on, then run the road trip fuel calculator twice: once with your usual economy and once with the AC-on figure. The difference is the cost of staying cool.
Does the AC affect electric cars too?
Yes. It draws from the battery, which reduces range, particularly in very hot or very cold weather when the climate system works hardest.