How to use it
- Click Start the test and keep this tab in front of other windows for three seconds.
- Read the Refresh rate card. A value such as 60 Hz, 120 Hz or 144 Hz is named when it is close to a standard rate.
- If the result says the frames were uneven, close other programs and test again.
How the rate is measured
A web page asks the browser for an animation frame, and the browser calls the page once for each frame it draws, passing the time of that frame. The page records the times for three seconds. The gap between two frames is the period of the screen refresh, and the rate in hertz is 1000 divided by that gap in milliseconds.
The gaps are measured in milliseconds and sorted, and the median gap is used, so an occasional long pause does not change the result. A gap longer than 100 milliseconds is a pause, not a frame, and is left out. The result is named after a standard rate (24, 30, 50, 60, 75, 90, 100, 120, 144, 165, 240 or 360 Hz) when it is within 4 per cent of it.
What the result can and cannot show
The result is the rate at which the browser draws frames during the test. A screen set to 120 Hz in its settings can draw at a lower rate on battery saver, while a power-saving or variable refresh display changes its rate with the content. A hidden tab is not drawn, so the test needs this tab in front.
The test does not check the cable, the graphics driver or the panel itself, and it does not show how smooth a game feels. A steady result of 120 Hz means the browser drew 120 frames a second in the test, which is the rate the screen can show at that moment.
Example: frames 16.7 ms apart
When the frames come 16.7 milliseconds apart, the period is 16.7 milliseconds and the rate is 1000 divided by 16.7, which is 59.9 Hz. That is within 4 per cent of 60 Hz, so the result reads 60 Hz. Frames 8.3 milliseconds apart give 120 Hz, and frames 6.9 milliseconds apart give 144 Hz.
Frequently asked questions
Why does my 144 Hz monitor show 60 Hz?
The rate of the frames the browser draws can be lower than the rate the monitor can show. Battery saver, a power-saving mode or a lower refresh rate set in your system can keep the browser at a lower rate. Check the refresh rate setting of your operating system and try again on mains power.
Is the test accurate enough to check my monitor?
It is a quick check of the frame rate the browser draws in three seconds. It is not a calibrated measurement, and it cannot prove that the panel and cable deliver the rate in its specification. Use it to see whether the screen runs at the rate you expect.
Is anything sent or stored by this test?
No. The times of the frames are kept in the page while the test runs and are dropped when the result is shown. Nothing is sent to a server, and nothing is saved on your device.
Why must the tab stay in front?
Browsers do not draw frames for a hidden tab, and they may slow the frames of a page that is not visible. The test then has no frames to measure, and it says so. Keep the tab in front and avoid switching windows during the three seconds.
What is a hertz?
A hertz is one cycle per second. A screen refreshed at 60 Hz redraws its image 60 times every second, which is one frame every 16.7 milliseconds.
Sources
- WHATWG HTML: animation frames and requestAnimationFrame
- W3C: requestAnimationFrame timing (the working group note; a hidden page is not sampled and may be throttled)
Figures and text last checked on Tuesday, November 10, 2026.