What the result actually measures
The browser draws a page once per screen refresh and says when each frame starts. The test collects five seconds of those frame times, takes the median interval — 6.94 ms at 144 Hz, 4.17 ms at 240 Hz — and counts every frame that took more than 1.6 times as long as a dropped one.
Measurement boundary: It measures what the browser gets from the display right now, not the panel’s maximum. Energy-saving modes, a battery, a background tab, the cable or port and variable refresh can all lower or blur it. Response time and motion blur are properties of the panel that no browser test can measure.
How to interpret the output
The rate is lower than the monitor’s
The most common finding: a 144 or 240 Hz monitor running at 60 Hz because the operating system was never told otherwise. On Windows 11, Settings → System → Display → Advanced display → Choose a refresh rate; on macOS, System Settings → Displays → Refresh rate.
Dropped frames
A few in five seconds are normal in a browser. Many, or a strip full of tall bars, mean the computer is not keeping up: a heavy tab, a busy background process or a power-saving limit.
Between two standards
A reading like 72 or 110 Hz usually means variable refresh or a power mode is changing the rate while you measure. Turn it off for the test, or measure again on mains power.
Troubleshooting unexpected results
It says 60 Hz on a faster monitor
Set the refresh rate in the operating system first. If it cannot be raised, the cable or port is the limit: use DisplayPort, or the HDMI port and cable the monitor’s manual names for high refresh.
It says 30 Hz
An energy saver is capping the browser or the laptop. Plug the laptop in, switch off the browser’s energy saver and battery saver, and measure again.
The result changes when I move the window
That is correct: the browser follows the refresh rate of the display the window is on. Measure each monitor with the window on it.
Frequently asked questions
How do I check if my monitor is running at 144 Hz?
Run the test with this window on that monitor. A reading close to 144 Hz with a median frame time near 6.94 ms means it is; 60 Hz means the operating system or the cable is holding it back.
Why does my 120 Hz phone show 60 Hz?
Low-power modes cap the screen at 60 Hz, and some mobile browsers limit web pages to 60 frames a second even on faster screens. The phone may still run games at 120 Hz.
What is frame skipping?
A frame the display never shows, so motion jumps. The test counts frames that arrived late in the browser; a monitor that skips frames when overclocked needs a camera test, which is beyond what a page can see.
Does variable refresh (G-Sync, FreeSync) affect the result?
It can. A browser window usually runs at the fixed maximum rate, but if variable refresh is active for it, the rate follows the frames the page draws and the reading may sit between standards.
