I installed a shader for Minecraft for the first time and I wanted to check how my computer was handling it, so I opened up NVIDIA’s Performance Overlay to see. It showed the FPS as a stable 59-60, but below it, something called “99% FPS” was swaying between 46 and 51. What does this mean, how does it differ from regular FPS?
It’s one type of “minimum FPS” number, because the game does not always run at the exact same framerate.
The absolute minimum FPS can actually be extremely low if you include brief glitches while textures are loading, etc. So to get a practical, useful “minimum” they give a number that the game runs at 99% of the time. It could be slower than this 0.5% of the time, and it would not drag this number down.
You can also measure 99.9% FPS, which will tell you the slowest the game runs 0.1% of the time, or you could even record the slowest FPS the game ever runs at any point. But 99% FPS is seen as a reasonable measure of “minimum” performance most of the time.
It’s a statistics thing. If you place all the FPSs you hit and scale according to how often they appeared, you can cut a line at any point and measure how many times the FPS fell below that line and how many times it went over.
The FPS threshold under which only 1% of the time your PC fell below was that number.
The average render throughput is 59-60 FPS. Because this is an average, there will be frames that were quicker and frames that were slower.
The 99% FPS is the throughput if every frame was as slow as the remaining slowest frame if the 1% of slowest frames is ignored.
Or inverting the numbers, a 99% FPS of 46 means that 99% of the frames took 22ms or less to render.
It can be a bit confusing, but the FPS you normally see is the average frames per second you’re seeing. Some will be faster, some will be slower, but they average out to that number.
99th percentile is the minimum frame speed you should expect to see 99% of the time, as opposed to just “on average”. It basically means “you won’t see FPS lower than this, outside of an occasional hiccup”.
Frame rate isn’t always constant, and there will occasionally be variation depending on the exact circumstances involved.
As such, average frame rate alone isn’t always a complete picture of performance when making comparisons, and calculating a value where the frame rate is above most of the time can also provide insight to the performance at the worst of times.