Input lag on a monitor is the time it takes for it to process the signal sent from a computer or console and for the image to start appearing on the screen. Having low input lag is beneficial for gaming, particularly if your games require fast reactions. Most monitors have low enough input lag that you won't notice any delay during regular desktop use, but a few milliseconds of lag can be the difference between winning and losing your games.
We test the input lag by using a specialized tool, and we test for it at its native resolution at different refresh rates.
Test results
Test Methodology Coverage
While we've tested for input lag since our original Test Bench 1.0 in October 2017, the test has evolved over time. Results and scores are only comparable between monitors on Test Benches 1.2 and newer. Learn more about how our test benches and scoring system work.
| Tests | 1.0 | 1.1 | 1.2 and newer |
|---|---|---|---|
| Native Resolution @ Max Hz | ✅ | ✅ | ✅ |
| Native Resolution @ 120Hz | ❌ | ❌ | ✅ |
| Native Resolution @ 60Hz | ✅ | ✅ | ✅ |
| Backlight Strobing (BFI) | ✅ | ✅ | ✅ |
| Non-Native Res @ Native Refresh Rate | ✅ | ❌ | ❌ |
| Variable Refresh Rate | ✅ | ✅ | ❌ |
| Variable Refresh Rate @ 60Hz | ❌ | ✅ | ❌ |
| 10-Bit HDR | ✅ | ✅ | ❌ |
When It Matters
When you're using a monitor, you want your actions to appear on the screen almost instantly, whether you're typing, clicking through websites, or gaming. If you have high input lag, you'll notice a delay from the time you input something on your keyboard or when you move your mouse to when it starts appearing on the screen. If it's bad enough, it can make the monitor almost unusable.
For gamers, low input lag is even more important because it can be the difference between winning and losing in games, especially those that need fast reactions. Although its input lag represents a small step in the system's total latency, you still want to ensure it has low input lag before worrying about the latency of your other devices.
When does the input lag become noticeable?
Any monitor adds at least a few milliseconds of input lag, but most of the time, it's small enough that you won't notice it at all. There are some cases where the input lag is so high that it becomes noticeable, but that's very rare and may not necessarily be caused only by the monitor. Your peripherals, like keyboards and mice, add more latency than the monitor, so if you notice any delay, it could be because of those and not your screen.
There's no definitive amount of input lag when people will start noticing it because everyone is different. A good estimate of around 30 ms is when it starts to become noticeable, but even a delay of 15-20 ms can be problematic for reaction-based games. You can try this tool that adds lag to estimate how much input lag bothers you, but keep in mind that this tool is relative and adds lag to the latency you already have.
Why there's input lag
Input lag comes from the fact that the monitor has to process the signal it receives and display it on screen. Although this usually happens within a few milliseconds, it's not instant. Before it even processes an image, there's your system's total latency that also adds delay. For example, your computer has to process and render the image on its end, and then there's latency from your mouse and keyboard that you also have to consider. Even your Internet connection has an impact on this, which is why online gaming can often feel sluggish. So, while your monitor has some input lag, it's usually a small amount in your system's total latency.
Our Tests
In our input lag tests, we use a dedicated photodiode device connected to a PC. We use a program to flash a white square in the middle of the screen and record the time it takes for the image to appear in the sensor. Keep in mind that the sensor stops reading the moment the image starts to appear on screen, and it isn't about when the screen fully displays it, which is related to the response time. We record multiple input lag measurements and take an average of them. Outliers aren't included in the measurement either.
Since monitors refresh the screen progressively from top to bottom, any new image reaches the center of the screen in the middle of the refresh rate cycle. It means that if a monitor has a refresh rate of 144Hz, the screen refreshes itself 144 times every second, and a new image appears every 6.94 ms. Since we're measuring the input lag at the center, it only takes 3.47 ms for the new frame to reach the middle. Any 144Hz monitor has a minimum input lag of 3.47 ms, so even if we measure an input lag of 4.0 ms, it's only 0.53 ms higher than the minimum, which is fantastic. Below is a table of the minimum input lag for the common refresh rates on monitors.
| Refresh rate | Time between frames | Minimum input lag |
|---|---|---|
| 60Hz | 16.67 ms | 8.33 ms |
| 120Hz | 8.33 ms | 4.17 ms |
| 144Hz | 6.94 ms | 3.47 ms |
| 165Hz | 6.06 ms | 3.03 ms |
| 180Hz | 5.56 ms | 2.78 ms |
| 240Hz | 4.17 ms | 2.09 ms |
| 360Hz | 2.78 ms | 1.39 ms |
| 540Hz | 1.85 ms | 0.93 ms |
As you can see, there are diminishing returns in input lag with higher refresh rate monitors. For example, the difference in minimum input lag between a 60Hz and 120Hz monitor is far greater than between 180Hz and 240Hz, even though they each have a 60Hz difference.
Native Resolution At Max Hz
This test represents the input lag of a monitor while using its max refresh rate at its native resolution, including any optional overclock settings. It tends to be the lowest input lag possible that the monitor has. To get the lowest amount of lag on some monitors, it might be necessary to enable a 'Game' or 'Instant' mode, but most monitors don't require any extra settings.
For monitors that have a dual-mode feature that boosts the refresh rate with a lower resolution, we still perform this test at the max refresh rate of its native resolution. We include additional input lag results in the text.
Native Resolution At 120Hz
We repeat the test at 120Hz, with the minimum input lag being 4.17 ms. This test result is important if your games are locked to 120Hz, whether it's on a PC or with a gaming console, like a PS5 or Xbox Series X|S. That said, if your game starts at a higher refresh rate and uses VRR to drop down to 120Hz, then the input lag you'll experience is that of the refresh rate the monitor originally starts at. So, if you have a 360Hz monitor and game at that refresh rate, the lag will remain low no matter how much the frame rate fluctuates.
Native Resolution At 60Hz
We repeat the test at 60Hz, with the minimum input lag being 8.33 ms. This test result is important if your games are locked to 60Hz, whether it's on a PC or with a gaming console. That said, if your game starts at a higher refresh rate and uses VRR to drop down to 60Hz, then the input lag you'll experience is that of the refresh rate the monitor originally starts at. So, if you have a 360Hz monitor and game at that refresh rate, the lag will remain low no matter how much the frame rate fluctuates.
Backlight Strobing (BFI)
Backlight strobing, also known as black frame insertion (BFI), is a feature some monitors have to reduce persistence blur at low refresh rates. It requires processing on the monitor's end, so it can add input lag, which is why we measure it. We test for the input lag with BFI enabled at the max possible refresh rate that the feature allows for. Sometimes, this is less than the monitor's max refresh rate, so it may seem that it has increased input lag with it on, when in fact it's using a different refresh rate.
Additional Information
Input Lag With VRR, HDR, And Non-Native Resolutions
A monitor's input lag is rarely impacted by other factors, such as whether you're using VRR or HDR. Prior to Test Bench 1.2, we tested the input lag with VRR and HDR enabled, but we found that it was rarely different from that without using these features. Even using local dimming doesn't significantly impact the input lag. Another thing to note is that the input lag remains the same no matter which connection you use, whether it's HDMI or DisplayPort, provided that they both achieve the same signals.
However, using a lower resolution than the native resolution does have an impact on input lag, as the monitor needs to upscale the image. We've seen this on dual-mode monitors, like the LG 39GX950B-B, whose results you can see below. However, the main trade-off of using these dual modes is that they have a higher max refresh rate, leading to a more responsive feel.
| Test | Native Resolution 5k2k |
Dual-Mode Resolution 2560x1080 |
|---|---|---|
| 330Hz | - | 2.3 ms |
| 165Hz | 3.9 ms | - |
| 120Hz | 5.1 ms | 7.5 ms |
| 60Hz | 9.7 ms | 16.1 ms |
Another thing to remember is that monitors don't have as much processing as TVs, so they tend to have lower input lag. So, if you want the lowest input lag possible for gaming, it's usually better to get a monitor. However, there are monitors that have higher input lag than TVs, so it's important to always do research.
Also see our recommendations for the best gaming monitors.
Difference Between Input Lag and Response Time
Some people get confused between the response time and input lag. Although they're important factors for gaming, they represent different things. While the input lag is the time it takes for the monitor to register an input from an external source and start transitioning colors, its response time is the time it takes for pixels to completely transition between colors. Essentially, from the moment you press a key on your keyboard until your monitor receives the signal, the input lag is the time it takes for the pixels to be activated and start their color transition. The response time is measured after that, so input lag and response time are measured one after another in the image processing chain of events. Although a monitor can have low input lag, it doesn't mean that it has a fast response time, and vice versa.
Learn more about response time
Other ways of measuring input lag
There's no one correct way to measure input lag. Our testing requires a specialized tool that not everyone has. If you're curious about what the input lag of your monitor is and you don't have the proper tools, there are simpler ways. You can connect your laptop to the monitor, or a computer connected to two screens, provided you know the input lag of one screen. You then display a timer on both screens at once (preferably one with milliseconds included), and you take a picture of the screens; the difference is your monitor's input lag. The time on the laptop will be higher than the time displayed on the monitor. In this image example, it has an input lag of 40 ms (1:06:260 – 1:06:220).
This is, however, an approximation because your computer doesn't necessarily output both signals at once. It's also not very accurate because it depends on your camera's shutter speed and whether you can capture the correct frame within the time limit. It can give you a good indication, though. It's also useful for comparing the input lag of two monitors if you use the same laptop.
If you have the proper tools, you may still measure input lag differently than what we do. For example, if you place a tool at the bottom or top of the screen, you'll get a different result than us. This is why you shouldn't compare our results with those of other reviewers.
How To Get The Best Results
As all monitors exhibit some sort of input lag, it's hard to truly improve it. There are ways to ensure you're getting the lowest possible input lag, though:
- Set the monitor to Game or Instant Mode, if it has that, but most likely any picture mode is good enough. This is mainly an issue for LG monitors, which have increased input lag in non-gaming modes.
- Use the highest possible refresh rate that your source supports. Gaming at the monitor's max refresh rate is ideal.
- Enable upscaling from your graphics card instead of the monitor.
If you want to lower the system's total latency, using wired keyboard/mice and a wired Internet connection can help ensure low latency.
Conclusion
Input lag is the amount of time it takes for your monitor to display an image or input on the screen from when it receives it. It's mostly important for competitive gamers who need fast reactions, but you can also notice a delay when the input lag is high during regular desktop use. We measure a monitor's input lag at its max refresh rate, at 120Hz, and at 60Hz, as well as with its BFI feature enabled, if it has one. Generally speaking, most monitors have low enough input lag for a responsive feel, but there are a handful that don't.