60 Hz, a quarter of 240One frame lasts 16.67 ms, as long as four frames at 240. Pick it to read a count against 60 instead: a match is 58.2 to 61.8 frames a second.
120 Hz, half of 240One frame lasts 8.33 ms, as long as two frames at 240. Pick it to read a count against 120 instead: a match is 116.4 to 123.6 frames a second.
144 Hz, 96 under 240One frame lasts 6.94 ms. 144 is three fifths of 240, so the page names a count of 144 as a rate of its own, not as 240 with frames missing. A match is 139.7 to 148.3 frames a second.
165 Hz, 75 under 240One frame lasts 6.06 ms, 1.89 ms longer than a frame at 240. Pick it to read a count against 165 instead: a match is about 160 to 170 frames a second.
240 Hz, this page's rateOne frame lasts 4.17 ms, which is 1,000 divided by 240. A count from 232.8 to 247.2 frames a second, 3 percent either side of 240, is read as a match.
Show all 16 rates and readings (11 more)
What a count against 240 means 5
60 where 240 was expected60 is a quarter of 240. Some browsers hold every page near 60 frames a second by default, so a 60 here is the browser's rate and by itself says nothing about the screen. Count again in a second browser and compare.
120 where 240 was expected120 is exactly half of 240. With 240 picked, a count of 120 means the usual frame lasted 8.33 ms, the length of two frames at 240. The count cannot say why. Close other tabs, count again, and see whether the next result reads the same.
A count that matches 240With 240 picked, a match is a count between 232.8 and 247.2 frames a second: about one frame every 4.17 ms for the whole count. It is the browser's rate on this screen, which is as much as a web page can read.
An uneven pace at 240The page calls the pace uneven when fewer than nine frames in ten are within a quarter of the usual length: from 3.13 to 5.21 ms at 240. Where a browser's clock is too coarse to time single frames, the page says so and gives only the average.
Frames dropped at 240A frame counts as dropped when it lasts more than one and a half times the usual frame: over 6.25 ms when the usual one is 4.17 ms. The page reports them once about one frame in 200 is missing, 11 or more in a ten-second count at 240.
What is drawn during a count 3
Graph with its line at 4.17 msOne column for each frame, as tall as the frame was long, with a grey line a third of the way up at 4.17 ms. A column twice that height is a frame of 8.33 ms. Nothing slides across in this view.
Lanes at 240, 120 and 60Three blocks move together during a count. The top one is redrawn every frame, the middle one every second frame and the bottom one every fourth: at a clean 240, that is 240, 120 and 60 pictures a second side by side.
Strip at 240 steps a secondDuring a count a bar crosses the picture, moved one step for every frame the browser draws: 240 steps a second at a clean 240. Even steps mean even frames. A visible jump is a frame that never came.
240 Hz in numbers 3
240 is a whole multiple of 24, 30, 60 and 120240 divides by 24 ten times, by 30 eight times, by 60 four times and by 120 twice. Film at 24 pictures a second and video at 30 or 60 each fill a whole number of frames at 240.
A ten-second count at 240 keeps about 2,280 framesThe page leaves out the first half second of every count, so ten seconds keep 9.5: about 2,280 frames at 240, not 2,400. The line under the figure prints the frames and the seconds it kept.
An early 240 Hz monitor came out in 2017One of the first monitors to refresh 240 times a second was released in 2017, five years after the first 144 Hz displays. At 240 Hz a picture stays up for about 4.2 ms, against 6.9 ms at 144 and 16.7 ms at 60.
How this list was compiled: Written for this page. Every frame length, band and frame count here is arithmetic, worked out: a frame lasts 1,000 ms divided by the rate, a match is 3 percent either side of the rate, and a ten-second count keeps 9.5 seconds. That a browser's animation callbacks generally match the display refresh rate, that most browsers pause them in background tabs, and that their timestamp has a minimal precision of 1 ms, is from https://developer.mozilla.org/en-US/docs/Web/API/Window/requestAnimationFrame, read 2026-10-06. That refresh rate is how often a display shows a new image and can be independent of frame rate, that films are usually shot at 24 frames a second, that 144 Hz displays first appeared in 2012, and that one of the first 240 Hz monitors was released in 2017 and holds a picture for about 4.2 ms, is from https://en.wikipedia.org/wiki/Refresh_rate, read 2026-10-06; Wikipedia text is under CC BY-SA 4.0 and is restated here in this site's own words. That one browser engine's setting to prefer page updates near 60 frames a second is on by default on three operating systems is from WebKit bug 173434, https://bugs.webkit.org/show_bug.cgi?id=173434 (open, last changed 2026-05-19), read 2026-10-06. The page counts how often the browser draws, which can be lower than the rate of the screen. Nothing here measures a monitor. Licence: own work
How it works
On a 240 Hz screen this 240 hz test can still read 120 or 60: the number is the rate your browser draws at, and the page names which.
Read the full guide
How to run the 240 Hz test
1. Leave 240 Hz lit and press Start.
2. Keep this tab in front for ten seconds. Switching tabs throws the count away.
3. Read the figure and the line under it: a match, half rate, 60, or another rate by name.
4. Change one thing, such as the browser, and count again. Your last ten counts stay listed on this device.
Questions and answers
Does a 240 hz test measure the monitor or the browser?
The browser. The page counts the frames your browser draws, which generally follow the screen's refresh rate. A browser can draw fewer frames than the screen shows, so a low count is not proof of a slow screen.
Is a 240 fps test the same as a 240hz test?
On this page, yes. Hz counts how often a screen shows a new picture; fps counts how many pictures are made for it. The page counts your browser's frames a second and reads them against 240 under either name.
Why does my 240 Hz test read 144 or 165?
Because the browser is drawing at that rate. 144 and 165 are rates of their own, so the page names the count as one of them where 240 was expected. Pick that rate to read the next count against it.
How accurate is a 240 hz test in a browser?
Accurate as an average, not frame by frame. A browser may round frame times to a whole millisecond, about a quarter of a frame at 240 Hz, so the page divides the whole count by its length and shows one decimal place.