RAIL Performance Model
RAIL stands for response, animation, idle and load.
Response time limits
- 100 milliseconds. Respond to a user action within this time window and they will feel like the result is immediate. Any longer and that connection between action and reaction breaks.
- 1 second. Within this window, things feel part of a natural and continuous progression of tasks. Beyond it, the user will lose focus on the task they were performing. For most users on the web, loading a page or changing views represents a task.
- 16 milliseconds. Given a screen that is updating 60 times per second, this window represents the time to get a single frame to the screen (Professor Math says 1000 ÷ 60 = ~16). People are exceptionally good at tracking motion, and they dislike it when their expectation of motion isn’t met, either through variable frame rates or periodic halting.