Windows Down or Air Conditioning: What’s Better When Driving?

It depends on speed and conditions: below roughly 40–45 mph (65–70 km/h), driving with the windows down is usually more efficient; above that, using the air conditioner typically wastes less energy than the added aerodynamic drag from open windows. The better choice also varies with heat, humidity, vehicle type, and whether you drive a gas car or an EV, but comfort and safety should take priority in extreme temperatures.

The science behind the trade-off

Rolling down the windows reduces the need for the AC compressor but increases aerodynamic drag, especially at higher speeds as airflow becomes turbulent around open window frames. Using air conditioning adds a mechanical or electrical load: in combustion cars the compressor draws power from the engine (raising fuel use), while in EVs it draws from the battery (reducing range). Independent tests and SAE research consistently show a speed-dependent “crossover”: at city speeds, open windows often beat AC; on highways, AC usually wins on efficiency.

How speed changes the answer

The following rules of thumb reflect common test results across sedans, SUVs, and pickups; your exact break-even point can vary with aerodynamics, cabin size, and AC settings.

• Stop-and-go city (under ~25 mph / 40 km/h): Windows down is generally most efficient; AC load is a large share of energy at low speeds.
• Urban/suburban (25–45 mph / 40–70 km/h): It’s a toss-up; light AC or vent/fan with partially open windows can be optimal. Heavier vehicles and boxier shapes favor using AC a bit sooner.
• Highway (55–75 mph / 90–120 km/h): Use AC. The drag penalty from open windows typically exceeds the compressor’s energy use, particularly in taller vehicles and trucks.
• Very high speeds (75+ mph / 120+ km/h): AC is clearly more efficient; open windows can significantly increase drag and noise.

In practice, aim to use ventilation or open windows at low speeds, transition to AC in the 40–50 mph range, and stay with AC on the highway—adjusting for comfort, humidity, and air quality.

Other factors that tip the balance

Beyond speed, several conditions can shift the efficiency calculus one way or the other.

• Heat and humidity: Higher heat loads and humid air demand more AC power; windows may feel ineffective in sweltering, humid conditions.
• Vehicle shape: Boxy SUVs and pickups suffer a larger drag penalty with windows down than slippery sedans or coupes.
• Window choice: Cracking rear windows or using flow-through vents reduces buffeting and can lessen drag versus dropping all front windows.
• Sun exposure: Dark interiors and big glass areas increase cooling load; sunshades and tint (where legal) reduce AC demand.
• Air quality: In heavy traffic or smoky/polluted areas, AC with recirculation protects occupants and can be more efficient than drawing hot, dirty outside air.
• Cabin occupancy: More people add heat and humidity; AC becomes more effective versus windows.

If conditions amplify either aerodynamic drag or cooling load, the break-even speed moves: harsher heat and humidity push you toward AC sooner; more streamlined cars let you use windows at slightly higher speeds without as much penalty.

Real-world fuel and range impacts

Gasoline and diesel vehicles

Modern AC systems can increase fuel consumption anywhere from about 5% to 20% depending on ambient temperature, sun load, vehicle size, and settings (aggressive cooling and big cabins sit at the high end). Opening windows at highway speeds can increase fuel use on the order of a few percent in slippery sedans and notably more in taller, boxier vehicles. Tests often find a crossover near 45 mph (70 km/h): below it, windows are usually better; above it, AC typically uses less fuel overall.

Electric vehicles

AC draw in EVs commonly peaks around 2–5 kW when first cooling a hot cabin, settling to roughly 0.5–2 kW. In hot weather, AC typically reduces range by about 5–10% in steady driving, less at higher highway speeds where propulsion dominates energy use. As with gas cars, open windows cause significant drag at speed, so the same speed-based guidance applies. Preconditioning while plugged in, using recirculation, and moderating fan/temperature settings can minimize range loss.

How to stay cool efficiently

These practical steps help you maintain comfort while minimizing fuel or range penalties in both gas cars and EVs.

• Pre-cool and purge: Park in the shade or use a sunshade; before turning on AC, open windows briefly to vent hot air, then close and cool.
• Use Auto and recirculate: Auto climate control optimizes compressor and fan use; recirculation cools already-cooled cabin air and reduces load, especially in traffic.
• Dial in moderate settings: Set a reasonable temperature (e.g., 72–76°F / 22–24°C) and avoid max-cool unless necessary—small changes can save energy.
• Leverage ventilation: At low speeds, use fan-only or crack rear windows to create flow-through ventilation with less buffeting and drag.
• Target occupants: Use seat ventilation or cooled seats if available; they provide comfort at lower overall AC output.
• Maintain the system: Keep the cabin air filter clean and service the AC to maintain efficiency; a struggling system wastes energy.
• For EVs: Precondition while plugged in, and use eco/efficiency HVAC modes to limit peak loads.

Combining preconditioning, smart HVAC settings, and selective window use usually yields the best comfort-to-efficiency balance across seasons and drive cycles.

Safety and comfort come first

In extreme heat, preventing heat stress and maintaining alertness outweigh small efficiency gains. If the cabin is uncomfortable or air quality is poor, use the AC and recirculation. Also consider noise and buffeting with windows down, which can increase fatigue on longer trips.

Bottom line

Use windows at low speeds and AC at highway speeds, adjusting for heat, humidity, vehicle type, and air quality. For most drivers, transitioning to AC around 40–45 mph maximizes efficiency without sacrificing comfort.

Summary

Below ~40–45 mph, open windows typically save energy; above that, AC is usually more efficient due to the drag penalty of open windows. Hotter, more humid conditions and boxier vehicles push you toward AC sooner. Pre-cooling, recirculation, moderate settings, and smart ventilation can keep you comfortable while minimizing fuel or range loss—and safety should always take priority.

Is driving with windows down bad for gas mileage?

Having your windows down wastes more gas than running the air conditioner at highway speeds (typically above 40-50 mph) due to increased aerodynamic drag, but it is more fuel-efficient at lower, city-like speeds where the load on the engine from the A/C is more significant than the minimal drag from open windows. 
Why wind resistance matters

• Aerodynamic Drag: Opens in new tabAt higher speeds, open windows create significant air resistance, or drag, making the engine work harder to maintain speed and consume more fuel. 
• Engine Strain: Opens in new tabWhile modern A/C systems are efficient, the added load on the engine by the A/C compressor at lower speeds can consume more fuel than the drag from open windows. 

When to choose open windows vs. A/C

• Lower Speeds (City Driving): Opens in new tabRoll down your windows for better fuel efficiency. The drag from open windows is minimal at these speeds, and the A/C’s strain on the engine can be more costly. 
• Higher Speeds (Highway Driving): Opens in new tabUse the air conditioning with the windows up. The significant drag from open windows at these higher speeds increases fuel consumption much more than the load from the A/C system. 

In summary 

• Low speeds: Open windows are generally more fuel-efficient.
• High speeds: Use the air conditioning for better gas mileage.

What uses more gas driving with AC or windows down?

While all this might seem like a minor issue, getting it wrong can have a notable impact on your fuel economy; using AC can increase your fuel consumption by as much as 10% but opening the windows at higher speeds can increase fuel consumption by as much as 20%.

Is it better to have windows down or AC MythBusters?

MythBusters found that at lower, urban speeds (like 45 mph), running the air conditioner is less fuel-efficient than having the windows down, as the drag from the open windows has less of a negative impact at slower speeds compared to the engine load from the AC. At highway speeds, however, the opposite is true: the drag from open windows significantly increases and outweighs the load of the air conditioner, making AC more fuel-efficient.
 
You can watch this video to see an overview of the MythBusters experiment: 34sxXMetalicDustXxYouTube · Mar 9, 2011
MythBusters’ Experiment and Findings 

• The Test: The MythBusters team used two identical SUVs, driving them at 45 mph until their fuel ran out.
• The Setup: One SUV had the windows rolled down and AC off, while the other had the windows up and AC on full.
• The Result: The SUV with the windows down ran significantly further than the one with the AC on, showing that at 45 mph, using the AC was less fuel-efficient.

Why the Difference at Different Speeds

• At Lower Speeds (City Driving): Opens in new tabThe increase in aerodynamic drag from open windows is less significant, making the AC’s load on the engine the primary factor in fuel consumption. 
• At Higher Speeds (Highway Driving): Opens in new tabThe aerodynamic drag from open windows dramatically increases, creating much more resistance and causing the engine to work harder, leading to greater fuel consumption than running the AC. 

The General Rule 

• Use the AC for highway speeds: to maintain better fuel efficiency.
• Roll down the windows: at city speeds or in stop-and-go traffic to conserve fuel.

Is it better to drive with AC or windows down?

Driving with the windows down is more fuel-efficient at low speeds (under 50 mph), while using the air conditioning (AC) is more fuel-efficient at high speeds (above 50 mph). At low speeds, the drag from open windows is minimal, and the AC’s power usage is a greater fuel drain. At highway speeds, the aerodynamic drag created by open windows significantly impacts fuel economy, outweighing the fuel consumed by the AC system. 
When to Roll Down the Windows

• Low Speeds: When driving at city speeds or in stop-and-go traffic (below approximately 50 mph), rolling down the windows is often more fuel-efficient than using the AC. 
• Better Air Quality: At low speeds, you can get fresh air without excessive noise or air pollution, and the airflow can help clear the cabin of chemicals from interior materials. 

This video explains how opening your windows at low speeds is more fuel efficient: 59sBjørn NylandYouTube · May 14, 2018
When to Use the Air Conditioning

• Highway Speeds: Opens in new tabAt higher speeds (above approximately 50 mph), the drag from open windows creates more resistance than the AC uses, making it more fuel-efficient to keep the windows up and the AC on. 
• Clean Air and Comfort: Opens in new tabAC provides a more pleasant and less stressful driving experience by maintaining a consistent, comfortable temperature and filtering out dust, fumes, and other pollutants from the outside air. 
• Defogging Windows: Opens in new tabThe AC system also removes moisture from the air, which is essential for defogging windows on humid or rainy days, improving visibility.