Frame rate is time between images
Every frame rate hides a time. Divide 1000 by the frames per second and you get the milliseconds each frame takes:
- 24 fps: 41.67 ms
- 30 fps: 33.33 ms
- 60 fps: 16.67 ms
- 120 fps: 8.33 ms
- 240 fps: 4.17 ms
Below about 10 to 12 images a second you see separate pictures. Above that your eye reads them as motion. For games, 60 fps has long been treated as the minimum for smooth play. Frame time matters as much as the average, though. A game can average 60 fps and still look choppy if some frames take much longer than others.
Why film runs at 24
24 fps isn't a law of nature. Early silent films had stated frame rates anywhere from 16 to 24 fps, and when sound arrived in the late 1920s the industry settled on 24 as a middle ground. Between 1927 and 1930 it became the standard for 35 mm sound film.
TV rates have their own history. They followed the power grid, with 60 in some countries and 50 in others. When color TV arrived, the 60 had to drop by 0.1% to reduce a picture artifact called dot crawl. That's why standards in North America, Japan and South Korea are built on 60/1.001, which is 59.94 images per second.
Two clocks that don't match
A game makes frames and a screen shows them, and each runs on its own clock. Frame rate is how fast your system generates frames. Refresh rate is how often the display shows a finished one. Say your graphics card makes 90 fps, one frame every 11.11 ms, and the monitor refreshes at 144 Hz, every 6.94 ms. Frames arrive slower than refreshes, so some refreshes have no new frame to show. A fixed refresh screen then repeats a frame, which looks like judder, or switches mid refresh, which tears. VRR fixes this by making the refresh follow the frames.
The lower of the two numbers is the one you see. A 240 Hz monitor can't show more than your graphics card makes, and a graphics card making 300 fps can't show more than a 144 Hz monitor refreshes.
Where more FPS stops paying off
Each step up saves less time. Going from 30 to 60 fps cuts 16.67 ms from every frame, from 60 to 120 it cuts 8.33 ms and from 120 to 240 it cuts 4.17 ms. Higher rates still reduce blur on moving objects and lower input lag, and the gain is real. It's just a smaller slice each time, and some people have trouble telling high frame rates apart at all.
So spend your graphics budget where it shows. A steady 60 or 120 fps with even frame times often feels better than a higher average that swings.