Diablo 3: How to Check FPS (Frames Per Second)
In Diablo 3 for the PC, if you’re worried about your FPS (Frames Per Second), or in other words, how well your computer is running the game, you can turn on the FPS counter.
By default, turning on the FPS counter is mapped to Ctrl+R. You can change this setting in the Key Bindings section.
When you turn on FPS, it will place the counter in the top left hand corner, directly above the picture of your follower if you have one at the time.