How the refresh rate is measured
Browsers draw animation in step with the display. Every time the screen is ready for a new image, the browser calls requestAnimationFrame, and this page records the exact time of each call. On a 60 Hz monitor the gap between frames is about 16.7 milliseconds, on 120 Hz about 8.3 ms, on 144 Hz about 6.9 ms and on 240 Hz about 4.2 ms. The tool takes the median gap of the last several hundred frames, converts it to frames per second and snaps it to the nearest common refresh rate when it is within a few percent.
Why the number may be lower than your monitor's rating
- The display is set to a lower mode. Many 144 Hz monitors ship set to 60 Hz. Check the display settings of your operating system and the cable: an old HDMI cable or port may not carry high refresh rates.
- Battery saver or power mode. Laptops and phones often cap the rate at 60 Hz to save energy.
- Variable refresh and multi-monitor setups. With several screens the browser may follow the slowest one.
- Background tab or hidden window. Browsers slow down or pause animation that is not visible.
Frame times and dropped frames
Average FPS hides stutter, so the tool also shows the median frame time and the slowest 1% of frames. A dropped frame is counted whenever a gap is more than one and a half times the normal frame time, meaning at least one refresh passed without a new image. A few drops when you switch windows are normal; a steady stream suggests the browser or computer is overloaded, or that a heavy extension is running.
The moving pattern
The ball moves at a fixed speed in pixels per second. On a high refresh display it should look noticeably smoother than on 60 Hz. If it jumps or shows tearing, try closing other tabs or enabling hardware acceleration in your browser settings. This is a browser-level test: games run in their own engines and can reach different frame rates than a web page.