system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] How fast is "full impulse"? Does it vary from ship to ship?
gpt
Technically 'full impulse' is a throttle setting, not a speed.  Basically it's setting the impulse engines to full power, and whatever acceleration you get out of that is full impulse.

That said, there is a sort of convention among Starfleet vessels to limit overall sublight speed to 1/4 the speed of light.  So once your impulse engines get you going that fast, you typically throttle back.

Edit: Oh, and yes, it varies from ship to ship, as different ship classes have more or less powerful impulse engines.