Input Lag Test

This input lag test gives you two ways to measure the delay a screen adds, using a camera because a browser cannot see light leave a display. The photo timer shows a millisecond count that changes every frame. Show it on two screens at once, photograph both together, and the difference between the two readings is how much later one screen shows the same frame. The click to flash pad turns white the moment you press it, for counting frames in a slow motion video. It works for monitors, laptop screens, TVs and projectors, with any camera or phone, on Windows, macOS, Linux and ChromeOS.

How to compare two screens with the photo timer

1. Connect both screens to the same computer and duplicate them. On Windows, press Win + P and choose Duplicate. On a Mac, open System Settings, Displays, select the second display and choose Mirror in its Use as menu.
2. Set both screens to the same resolution and refresh rate if you can.
3. Open this page and press Full screen. The timer appears at the top, middle and bottom, since screens draw from top to bottom.
4. Set your camera or phone to a shutter speed of 1/1000 second or faster, in its manual or Pro mode, and frame both screens in one shot.
5. Take at least eight photos. For each one, type the middle reading of each screen into Screen A shows and Screen B shows, then press Add photo.
6. Read the average under Screen B behind A. If you know the lag of screen A, for example from a review, add it to get the lag of screen B.

When a photo catches a screen mid-change, two numbers overlap. Use the ten frame cells beside the timer: the brightest cell marks the newest frame, and the frame number underneath helps you match the two screens.

Measure the whole delay with slow motion video

The photo timer compares screens. To measure everything from your click to the light, including the mouse, the computer and the screen:

1. Switch to Click to flash and press Full screen.
2. Set your phone to slow motion at 240 frames per second, which gives one video frame every 4.17 ms.
3. Film the mouse button and the screen together while you click the pad ten times.
4. Step through the video frame by frame. Count the frames from the moment the button goes down to the first frame where the pad turns white, and multiply by 4.17 ms.
5. Average the ten clicks. The Page response readout shows how much of that time the browser itself took.

What the results mean

As a guide, most gaming monitors add about 1 to 5 ms at their top refresh rate, 60 Hz office monitors about 9 to 15 ms, TVs in game mode about 5 to 20 ms, and TVs outside game mode often 30 to 100 ms or more. Reviews usually measure in the middle of the screen, so compare middle readings.

Input lag and response time are different

Input lag is the wait before a new frame starts to appear: signal processing, scaling and the time to draw down to the part of the screen you are looking at. Response time is how long each pixel then takes to change color. Slow response shows as trails behind moving objects, which the ghosting test makes visible. A TV can have fast pixels and still feel slow because of processing, and a cheap monitor can respond quickly while ghosting badly.

How to reduce input lag on a TV

• Switch the picture mode to Game, or turn on Game Mode. Many TVs and consoles support Auto Low Latency Mode, which switches it on by itself.
• Turn off motion smoothing, such as TruMotion on LG, Picture Clarity or Auto Motion Plus on Samsung and Motionflow on Sony, and turn off noise reduction.
• Set the HDMI input type or icon to PC when you connect a computer. Many TVs then skip extra processing.
• Use the HDMI port marked for 4K at 120 Hz or for gaming, and run 120 Hz if your console or PC supports it.

How to reduce input lag on a PC monitor

• Run the highest refresh rate the monitor supports, and check it with the refresh rate test.
• Feed the monitor its native resolution so it does not have to scale the picture.
• Turn V-Sync off in fast games and use G-Sync or FreeSync with a frame rate cap a few fps below the refresh rate instead.
• Turn on NVIDIA Reflex or AMD Anti-Lag in games that offer them, which shorten the queue of frames waiting to be drawn.

Tools that measure input lag properly

For an absolute number in milliseconds you need a device that sends a known signal and senses the light. The Leo Bodnar lag tester sends a 1080p, 60 Hz picture and measures the delay at the top, middle and bottom of the screen; a 4K model also exists. The Time Sleuth does the same at retro console resolutions. Some G-Sync esports monitors include NVIDIA's Reflex Latency Analyzer, which measures from a compatible mouse click to the screen. Reviewers also use photodiode tools such as NVIDIA LDAT and the open source OSRTT.

What this input lag test cannot measure

The timer measures the difference between two screens, not the lag of one screen on its own, unless you know the lag of the other. Two video outputs are rarely started at exactly the same moment, so a single photo can be off by up to one refresh; averaging eight or more photos removes most of that error. Swapping the cables between the two screens and repeating removes the rest. To time your peripherals rather than the screen, use the mouse latency test, the input lag test keyboard page or the input lag test controller page, and to time yourself, try the reaction time test.

Input lag questions