Why use milliseconds instead of FPS?

Milliseconds add up. If rendering takes 8 ms and scripts 4 ms, you know what is left. FPS does not add.

What is a good split?

It depends on the game. Profile your own project, then set budgets from what you see.

Why is 30 to 60 FPS a bigger change than 60 to 90?

Frame time is the inverse of FPS: 30 to 60 saves 16.7 ms per frame, 60 to 90 only 5.6 ms. That is why the same optimisation looks bigger at low frame rates.

Should I leave headroom?

Yes. Aim for about 80% of the budget so spikes from loading, garbage collection or many enemies on screen don't drop frames.

Frame Time Budget Calculator: FPS to Milliseconds

A 60 FPS game has about 16.7 milliseconds per frame. Enter a target to see the budget and split it between your systems.

Target FPS

16.67 ms per frame

Measured frame time (ms)

50 FPS · over budget

Split the budget

Game logic and scripts35

5.83 ms

Rendering40

6.67 ms

Physics15

2.50 ms

Audio and other10

1.67 ms

Total: 100%

Frame time is more useful than FPS: it adds up, so you can give each system a budget.

When to use it

Hitting 60 FPS on modest PCs
Give rendering, scripts, physics and audio a slice of the 16.7 ms and profile each against its own number.
Planning for 120 Hz or VR
At 120 FPS the budget halves to about 8.3 ms; see which systems have to get cheaper.
Reading the profiler
Compare the milliseconds the Unity or Godot profiler reports with your budget instead of guessing from the FPS counter.