How Much MPG Do You Lose With the Windows Down?

Expect little to no loss at city speeds but a noticeable hit on the highway: roughly 0–2% below 35 mph, 2–8% around 55–65 mph, and 5–15% (or more for boxy vehicles) above 70 mph. The exact penalty depends on speed, vehicle shape, and how far the windows are open; at higher speeds, the drag from open windows can rival or even exceed the fuel use of moderate air-conditioning.

What the Data Shows

Opening windows increases aerodynamic drag, which grows rapidly with speed. Government efficiency guidance notes that open windows reduce fuel economy—especially on highways—because aerodynamic drag becomes a dominant load as speed rises. Independent tests and engineering studies have found small penalties at lower speeds and increasingly larger ones on fast roads, with wide variability by vehicle type and window opening.

Typical MPG Loss by Speed

The following ranges summarize what multiple tests and engineering analyses commonly observe for internal-combustion passenger vehicles in mild conditions, assuming front windows opened several inches:

• Under 35 mph (city driving): about 0–2% MPG loss
• 35–55 mph (suburban/arterial): about 1–4% MPG loss
• 55–65 mph (typical highway): about 2–8% MPG loss
• 70+ mph (fast highway): about 5–15% for streamlined cars; 10–20% for SUVs/trucks with higher frontal area

These are broad ranges, not guarantees. A small, slippery sedan with windows cracked may sit at the low end, while a tall, boxy SUV with multiple windows fully down can land at the high end.

Why Speed and Shape Matter

Aerodynamic drag rises roughly with the square of speed. Opening windows disturbs airflow and generally increases a vehicle’s drag coefficient (Cd). At 30–35 mph, the engine’s workload is driven more by rolling resistance and stop‑and‑go losses, so the MPG change from windows down is minimal. At 65–75 mph, aerodynamic loads dominate; increasing Cd even slightly can translate into a meaningful fuel penalty. Vehicle shape, roof height, crosswinds, and window opening size all influence how large that penalty is.

Windows Down vs. A/C: Which Uses More Fuel?

It depends on speed, vehicle, and climate. Air-conditioning adds a relatively steady mechanical load on the engine or accessory belt, while open windows add a load that scales with speed.

At lower speeds (city traffic), running with windows down typically uses less fuel than running the A/C. At highway speeds, the balance shifts: for many modern sedans and crossovers, windows up with moderate A/C is often as good as—or better for MPG than—windows down. For large SUVs and pickups at 70+ mph, the windows-down penalty can be larger still, because their frontal area and baseline drag are higher.

Authoritative efficiency guidance notes that A/C can significantly reduce fuel economy in extreme heat, particularly on short trips, while open windows raise drag and hurt highway MPG. In moderate weather at steady highway speeds, the MPG hit from modest A/C is frequently in the mid-single digits, comparable to the mid-to-high single‑digit hit from open windows; which one is “better” varies by vehicle and conditions.

Practical Rule of Thumb

Use these situational guidelines to minimize fuel use without sacrificing comfort:

• City and low-speed driving (≤35 mph): Open the windows and keep A/C use light or intermittent.
• Highway driving (≥55 mph): Close the windows; use moderate A/C instead of large window openings.
• If you must ventilate at speed: Crack front and rear windows slightly or use the sunroof tilt to reduce buffeting and drag versus fully open side windows.

These habits balance comfort and efficiency and typically yield better MPG across mixed driving.

Other Factors That Change the Answer

Several variables can increase or decrease the MPG penalty from open windows:

• Vehicle type and aerodynamics: Sleeker cars lose less; tall, boxy vehicles lose more.
• How much is open: Small cracks cost little; multiple windows fully down cost more.
• Speed and wind: Higher speeds and crosswinds magnify the penalty.
• Cabin layout and deflectors: Vent visors or a tilted sunroof can smooth airflow.
• A/C system efficiency: Newer, variable-displacement compressors can cut A/C’s fuel penalty.
• Payload and roof racks: Extra weight or external carriers compound overall fuel use.

Because these factors interact, two seemingly similar vehicles can produce different results under the same conditions.

How to Quantify It in Your Car

If you want a vehicle-specific answer, a simple A/B test on a calm day can reveal your own MPG change:

1. Pick a flat, low-traffic loop (10–20 miles) and set a steady target speed.
2. Warm up the vehicle fully to stabilize fluids and A/C performance.
3. Run one pass with windows up and climate set to “vent” (A/C off); record indicated MPG (or fuel flow via an OBD-II app).
4. Run a second pass at the same speed with your typical window opening; record results.
5. Repeat in the opposite direction to cancel wind/grade, then average the pairs.
6. Optionally add a third set with windows up and A/C on a fixed, moderate setting.

This controlled comparison will show your car’s windows-down penalty and how it stacks up against moderate A/C use at that speed.

Summary

You typically lose little to nothing at city speeds with the windows down, a few percent at 55–65 mph, and potentially double‑digit MPG at 70+ mph—especially in larger, boxier vehicles or with multiple windows fully open. At highway speeds, closing the windows and using modest A/C often matches or beats the fuel use of driving with the windows down. Your exact result depends on speed, vehicle aerodynamics, and how far the windows are opened, so if you care about precision, test your own car under your usual conditions.

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 use 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. 

What is the 3 minute rule for air conditioners?

The 3-minute rule for air conditioners is a guideline that suggests waiting at least three minutes after turning the unit off before restarting it. This pause is crucial because it allows the refrigerant pressure in the system to stabilize, which prevents damage to the expensive compressor and helps the unit operate efficiently. Ignoring this rule can lead to short cycling, increased wear and tear, higher energy bills, and a shortened lifespan for your AC system. 
Why the 3-Minute Rule is Important

• Compressor Protection: Opens in new tabThe compressor builds pressure to circulate refrigerant. Restarting it immediately after a shutdown places extreme stress on it, which can lead to costly damage or failure. 
• Pressure Equalization: Opens in new tabWhen the AC is turned off, the pressure within the system needs time to equalize. The 3-minute wait allows this essential pressure stabilization to occur. 
• Prevents Short Cycling: Opens in new tabQuickly turning the AC on and off without allowing the system to fully stabilize is known as short cycling. The 3-minute rule prevents this, ensuring the unit completes its cooling cycles efficiently. 
• Enhances Efficiency: Opens in new tabBy allowing the system to stabilize, you ensure it restarts properly, leading to better energy efficiency and consistent performance. 

How to Apply the Rule

• Wait Before Restarting: If you’ve turned your air conditioner off, wait for a full three minutes before turning it back on. 
• Use Smart Thermostats: Many modern smart thermostats have a built-in delay feature that enforces this minimum runtime, making it easier to follow the rule. 

In summary, the 3-minute rule is a simple yet effective practice to protect your air conditioner’s compressor, prevent short cycling, and prolong the life of your system.

How much does windows down affect gas mileage?

20 percent
Unfortunately, the air flow creates resistance, increasing the work your engine must do to move your car down the road. Air resistance becomes a significant problem at high speeds. In fact, a Society of Automotive Engineers (SAE) study found that open windows reduce gas efficiency by 20 percent at 55 mph.