Windows Down vs. Air Conditioning: Which Uses More Gas?

It depends on speed and conditions: at low speeds, driving with the windows down usually uses less fuel than running the air conditioner; at highway speeds, using the AC with the windows up is typically more efficient. The reason is aerodynamic drag rises sharply with speed, while the AC’s compressor load is comparatively steady and more noticeable in city driving than on the open road.

How Speed Changes the Equation

Aerodynamic drag increases exponentially with vehicle speed. Cracking the windows at 20–35 mph barely changes airflow and has a small fuel penalty; at 60–75 mph, open windows disrupt the car’s streamlined shape and can increase drag enough to offset or exceed the fuel cost of running the AC. Meanwhile, AC draws power from the engine (or battery in hybrids/EVs), with its largest impact when the vehicle is moving slowly or idling—when there’s less engine power available and the compressor cycles harder to cool a hot cabin.

What independent tests and agencies report

Transportation and energy agencies, lab studies, and consumer tests converge on a practical rule: below roughly 40–45 mph, windows down tends to be more efficient; above about 50 mph, AC with windows up often uses less fuel. Measured impacts vary by vehicle and weather, but typical figures are: running AC can reduce fuel economy by roughly 5–20% in city conditions and somewhat less on the highway, while driving with windows down has a small penalty at urban speeds and a growing penalty at highway speeds that can equal or surpass AC use in some vehicles. Modern systems—like variable-displacement compressors and automatic climate control—can trim the AC penalty, while boxier vehicles and roof racks amplify the drag penalty of open windows.

When to Choose Windows vs. AC

The best choice shifts with speed, traffic, and heat load. Use the guidelines below to decide in real time.

• Stop-and-go or speeds under ~40–45 mph: Prefer windows down or fan-only ventilation; AC has a proportionally larger fuel impact here.
• Steady highway speeds above ~50 mph: Prefer AC with windows up; the drag from open windows often costs more fuel than the compressor.
• Moderate conditions (mild heat, short trips): Use outside air or fan; if you need cooling, brief AC bursts on recirculate can suffice.
• Very hot, humid days: AC will work hard at first; once the cabin cools, switch to recirculate and moderate the temperature to cut load.
• Vehicles with good aerodynamics (sedans) vs. high-drag shapes (SUVs/trucks): The drag penalty from open windows rises more on taller, boxier vehicles, favoring AC sooner on the speedometer.

These patterns reflect physics more than brand differences, but individual results vary by vehicle design, compressor efficiency, and how aggressively you cool the cabin.

How Much Fuel Are We Talking About?

Exact numbers depend on vehicle, weather, and driving style, but practical ranges from lab and road testing provide a sense of scale.

• AC impact (conventional gasoline cars): Roughly 5–10% fuel-economy reduction in typical warm weather; up to the mid-teens in very hot, humid, stop-and-go conditions.
• Windows-down impact: Minimal at city speeds; at 65–75 mph, the drag penalty can be modest to significant and, in some cases, comparable to or greater than running the AC.
• Hybrids: AC can have a larger effect in low-speed driving because the engine often shuts off; the compressor (electric on many hybrids) draws directly from the battery.
• EVs: AC reduces range modestly (tests commonly show single-digit to low-teens percent in hot weather). Open windows add little penalty at low speed but can cut range more at highway speed due to drag.

Treat these as ballpark expectations. For your car, a simple A/B test on a familiar route (reset trip computer, drive once with windows down, once with AC on) can show which choice wins under your conditions.

Practical Ways to Stay Cool and Save Fuel

Small adjustments can keep you comfortable while trimming the energy cost of cooling.

• Pre-cool smartly: When safe, open doors or windows briefly to vent hot air before starting the AC; hot-soaked cabins force the compressor to work hardest.
• Use recirculate after initial cool-down: Recirculating cooler cabin air reduces compressor load compared with constantly cooling hot outside air.
• Set a reasonable temperature: Each degree lower increases AC workload; many modern systems are most efficient near 72–76°F (22–24°C).
• Fan speed and vents: Higher fan speed moves cool air faster without always needing a colder setpoint; direct vents at occupants.
• Shade and tint: Use sunshades and, where legal, quality window tint to reduce solar load so the AC does less work.
• Keep the cabin filter clean: A clogged filter reduces airflow, making the system run harder.
• At highway speeds, keep windows mostly up: If you want fresh air, a small crack or using the vehicle’s vent setting has less aerodynamic penalty.

These steps reduce both the peak cooling demand and the sustained load, helping whichever choice—windows or AC—use less energy.

Other Variables That Can Tip the Balance

Beyond speed and temperature, a few factors influence whether windows or AC costs more fuel for you on a given day.

• Humidity: High humidity increases AC workload because the system must dehumidify air; windows may feel less effective in sticky conditions.
• Traffic patterns: Frequent stops amplify AC’s relative penalty; steady cruising amplifies the drag penalty of open windows.
• Vehicle design: Roof racks, open sunroofs, and boxy shapes magnify drag with windows down; sleek sedans suffer less but still see rising penalties with speed.
• Compressor technology: Newer variable or electric compressors can be more efficient than older on/off clutches, narrowing the AC penalty.

If your vehicle has an “eco” climate mode, it typically softens compressor demand in exchange for a slightly slower cool-down, improving efficiency in most daily driving.

Bottom Line

Use windows down at low speeds and AC at highway speeds if you’re optimizing for fuel. Modern AC systems are efficient enough that, once you’re above about 50 mph, keeping the windows up usually saves gas. In the city, ventilation or short, moderate AC use on recirculate is typically the thriftier choice.

Summary

At urban speeds, open windows generally beat AC for fuel economy; on the highway, AC with windows up is usually better due to reduced aerodynamic drag. Expect AC to cost roughly 5–10% in typical warm conditions (more in extreme heat or stop-and-go), while the windows-down penalty grows with speed and can equal or exceed AC by 65–75 mph. Use recirculate, reasonable temperature settings, pre-venting, and good shading to minimize energy use whichever option you choose.

Does using AC burn more fuel?

Yes, running your car’s air conditioning uses more gas because the engine must work harder to power the A/C compressor, creating an extra load that increases fuel consumption. The impact on gas mileage varies, with a noticeable decrease in stop-and-go city driving and a lesser effect at highway speeds. The decrease in fuel efficiency can be as much as 10% or more, depending on factors like outside temperature, driving conditions, and the vehicle’s make and model. 
How the A/C System Uses Fuel

• Engine-Driven Compressor: In most gasoline cars, a compressor runs off the engine’s serpentine belt, which is connected to the crankshaft. 
• Increased Engine Load: When the A/C is on, this extra load on the engine forces it to work harder to power the compressor and maintain the desired cabin temperature. 
• Fuel Consumption: To meet the higher demand, the engine consumes more fuel. 

Factors Affecting Fuel Usage

• Driving Conditions: The impact of A/C is more significant during city driving, with frequent stops and starts, compared to highway driving where the engine operates at a more consistent speed. 
• Speed: While driving with windows down may be more fuel-efficient at lower speeds, using the A/C at highway speeds can be more efficient due to the increased aerodynamic drag from open windows. 
• Car Model and Maintenance: Fuel efficiency drops differently for various car models. A well-maintained A/C system is also more efficient than one in poor condition. 
• Outside Temperature: The AC system demands more power when it’s very hot outside. 

Tips for Better Fuel Efficiency

• Use Wisely: Only use the A/C when necessary. 
• Start on Low: Begin with lower fan speeds and gradually increase them as needed. 
• Roll Down Windows at Low Speeds: At speeds under 35 mph, using the windows is often more fuel-efficient than using the AC. 
• Use the Recirculation Feature: This feature can help keep the cabin cool by recirculating the already cooled air, reducing the AC’s workload. 
• Park in the Shade: Parking in a shady spot or using a sunshade can reduce the car’s initial temperature, lessening the need for the AC to run on high settings for extended periods. 

Is it better to have windows down or AC to save gas?

To save gas, use the air conditioning (AC) at highway speeds (above 50-60 mph) and open your windows at lower city speeds. At high speeds, the increased aerodynamic drag from open windows uses more fuel than the AC system, which has a smaller impact on fuel economy. At lower speeds, the AC’s power draw is more significant, making open windows the more fuel-efficient choice. 
At Lower Speeds (City Driving) 

• Open your windows: Aerodynamic drag is less of a factor at lower speeds, and the energy required to run the AC compressor has a more significant impact on fuel efficiency.

At Highway Speeds (Above 50-60 mph)

• Use the AC with windows up: Opens in new tabAt higher speeds, the increased drag from open windows creates more resistance, which is worse for fuel economy than the load the AC compressor puts on the engine. 
• Use AC efficiently: Opens in new tabIf you must use the AC, consider setting it to the warmest temperature you can tolerate, recirculating the cooled air, and using the AC to get rid of heat before turning it on. 

Other Tips

• Ventilate before using AC: Opens in new tabBefore turning on the AC, roll down all the windows for a few minutes to let out hot air, which reduces the work your AC system needs to do. 
• Consider your vehicle type: Opens in new tabThe impact of open windows on fuel economy is more significant for larger, less aerodynamic vehicles compared to sleeker sedans. 

Is it bad to run car AC with windows down?

However, if the air conditioner runs simultaneously, opening the windows could make it harder to cool the car down. Keeping the A/C on and the windows open isn’t particularly economical. Running the air conditioner puts additional strain on the engine, which consumes fuel.

How much MPG do you lose with Windows down?

Driving with your windows down can negatively impact gas mileage due to increased aerodynamic drag, particularly at higher speeds. The effect varies by vehicle type and speed; a study by the Society of Automotive Engineers (SAE) found that opening windows on a sleek sedan reduced fuel efficiency by 20% at 55 mph, while an SUV saw an 8% reduction. A general rule of thumb is that opening windows is more fuel-efficient at lower city speeds, while using air conditioning is better at highway speeds. 
At Lower Speeds (City Driving)

• Benefit: Opening your windows is generally more fuel-efficient at low speeds because the aerodynamic drag created is minimal. 
• Reason: The added load on the engine from the AC system is often more significant than the small increase in drag from open windows. 

At Higher Speeds (Highway Driving)

• Detriment: Opening your windows dramatically increases aerodynamic drag. 
• Impact: This increased drag forces the engine to work harder to maintain speed, consuming more fuel. 
• Comparison: At speeds above 40-50 mph, the fuel penalty from open windows is often greater than the fuel used by the air conditioner. 

Factors Influencing the Effect

• Vehicle Aerodynamics: More aerodynamic cars, like sedans, experience a greater increase in drag with windows down compared to less aerodynamic vehicles like SUVs. 
• Speed: Drag increases significantly at higher speeds, making the impact of open windows more pronounced on the highway. 
• Vehicle Design: Newer vehicles are generally more aerodynamic, and their modern, efficient AC pumps may be more efficient than the drag caused by open windows at highway speeds. 

In Summary

• Below 40 mph: Open your windows for better gas mileage. 
• Above 50 mph: Use your air conditioner to save fuel.