Monitor response time test: refresh rate, response time and what you can measure

Four different numbers

• Refresh rate (Hz): how many times per second the monitor shows a new image. 60, 144, 240 Hz and so on.
• Frame rate (FPS): how many new images the computer or console produces per second. The monitor can only show as many as its refresh rate.
• Response time (ms): how long a pixel takes to change from one shade to another, often quoted as grey-to-grey (GtG). Slow transitions leave trails behind moving objects.
• Input lag (ms): the total delay from your input or the signal arriving to the image changing on screen.

A high refresh rate with slow response time still blurs; fast response time on a 60 Hz screen still looks less smooth than 144 Hz.

What a browser can show

• Refresh rate: the monitor refresh rate test counts how often the browser draws a frame. That usually matches the refresh rate the screen runs at, which is a quick way to check that a 144 Hz monitor is not stuck at 60.
• Ghosting and overshoot: the monitor ghosting test moves objects across the screen so you can see trails and bright or dark halos and compare overdrive settings by eye.
• Frame skipping: the frame skipping test lets a camera photo show whether an overclocked monitor really displays every frame.

What a browser cannot measure

A web page knows when it asked the browser to draw a frame. It does not know when the pixels on the panel finished changing. So browser timing cannot give you a response time in milliseconds, and it cannot measure input lag.

• Response time is measured with a photodiode or light sensor on the screen and an oscilloscope, or estimated with a high-speed or pursuit camera.
• Input lag is measured with a device that sends a signal and detects the change on screen, or a high-speed camera filming the input and the screen together.

Reviews that publish these numbers use such equipment. A page that prints a millisecond response time from browser timing alone is showing something else.

Ghosting, overshoot and motion blur

• Ghosting: a faint trail behind a moving object, caused by slow pixel transitions.
• Overshoot (inverse ghosting): a bright or coloured halo, caused by overdrive pushing the pixels too hard.
• Motion blur: the object looks soft even with fast pixels, because your eyes follow it while each frame is held still. Higher refresh rates and backlight strobing reduce it.

In the ghosting test, try each overdrive level in the monitor menu: the best setting is usually the one with the least trail and no obvious halo.

Choosing settings by eye

1. Set the highest refresh rate and confirm it with the refresh rate test.
2. Open the ghosting test at a speed similar to your games.
3. Step through each overdrive or response time setting in the monitor menu. Watch the trail behind the moving object and any bright or coloured halo.
4. Pick the setting with the shortest trail and no clear halo. Recheck at a lower refresh rate if you use variable refresh, because overdrive can look different when the rate drops.
5. If the monitor has backlight strobing (often called motion blur reduction), compare it too: motion looks sharper, but brightness drops and some people notice flicker.

Why a refresh rate test shows 60 Hz

1. The refresh rate is set to 60 in the system display settings. Choose the highest one available.
2. The cable or port does not support the rate at your resolution. Use DisplayPort or a suitable HDMI cable and port.
3. Power saving, battery mode or a laptop setting limits the rate.
4. The test tab is in the background or the window is on another monitor. Browsers slow down hidden tabs.
5. Variable refresh rate (G-Sync, FreeSync) can make the measured rate follow the content; measure on a static desktop.

Putting it together

To check a new gaming monitor, confirm the refresh rate, then compare overdrive settings in the ghosting test and pick the cleanest one. If the monitor is overclocked, check for frame skipping. For response time and input lag figures, rely on measurements from reviews done with proper equipment. The full checklist for a new screen is in how to test a new monitor.