Which is more fuel-efficient: AC or windows down?

When the weather outside is toasty hot we need to find a way to cool down while driving in our cars. Our options are usually either to turn on the air conditioning or to roll down the windows. Which of these options is the most fuel efficient?

Using the air conditioner does use some gas. The air conditioner draws its power from the engine, which runs on gas. In newer cars, this gas usage is tiny. To save on gas while running your air conditioner, consider turning it off while stopped in traffic or with your car in idle.

Driving with your windows down can actually use more gas than running your AC. Having the windows down can increase your car’s drag, which means your car has to work harder to keep going. To save on gas you could roll down the windows while stopped or sitting in traffic, but it’s a good idea to roll them up and turn on the AC when you start moving.