05 / 08
Device Latency — How Refresh Rate, Polling Rate and Bluetooth Add to Your Results
We calculate how much monitor refresh rate, mouse and keyboard polling rate, touchscreens and Bluetooth audio add to your reaction time measurements.
The result of a web reaction time test is human reaction time + device latency. You can't reduce device latency yourself, so knowing which factors add how much lets you read your results fairly.
Monitor refresh rate
The screen is redrawn at fixed intervals. Between the moment a signal is ready and the moment it actually appears on screen, up to one frame can pass.
| Refresh rate | One frame |
|---|---|
| 60 Hz | about 16.7 ms |
| 120 Hz | about 8.3 ms |
| 144 Hz | about 6.9 ms |
| 240 Hz | about 4.2 ms |
On top of this come the monitor's own signal processing time (input lag) and the time pixels take to change color (response time). This site measures your screen's frame interval at startup and shows it below your results.
Mouse and keyboard polling rate
USB input devices report their state to the computer at fixed intervals. A 125 Hz device may wait up to 8 ms, and a 1,000 Hz device up to 1 ms. Keyboards can also add a few ms depending on the switch type and debounce processing.
Touchscreens
Touchscreens tend to have more latency than a mouse because they must determine finger position and filter out jitter. This is a common reason phone results come out slower than computer results.
Bluetooth and audio
- Bluetooth mouse and keyboard — Because of the wireless transmission interval, latency can be higher and more erratic than with wired devices.
- Audio output — The operating system's audio buffer delays sound by a few to tens of ms. Bluetooth earbuds can be much slower depending on the codec, significantly inflating auditory mode results.
Browser and operating system
The browser receives input events, passes them to JavaScript, then composites and outputs the screen. If many tabs are open or the device is busy, this process can slow down. Power-saving mode also has an effect.
How to reduce latency
- Use a wired mouse, keyboard and earphones.
- Set the highest refresh rate available and turn on low-latency settings such as your monitor's "game mode".
- Close other tabs and heavy programs, and plug in your laptop.
- Above all, compare values measured on the same device. Device latency is nearly constant, so it doesn't get in the way of tracking your trend.