How to check FPS in Fortnite.
Follow these instructions from inside the Fortnite Battle Royale client. These steps were done on the PC version of the game:
1. From inside of Fortnite, head to the settings area. Do this by clicking the cog icon in the top right corner of the screen, located under the menu button.
2. At the top of the screen, make sure that you’re in the ‘Video’ tab, it’s the first screen that should be open.
3. Near the bottom of the menu, one of the options will be “Show FPS”. Ensure that this option is enabled.
4. When you head back into Fortnite, you can check your FPS in both the lobby and in-game. When playing, it can be seen just slightly to the left of the minimap.