Hi, thank you for taking interest in my generic TTRPG. When I was designing SMRPF I wanted it to be generic, so a square is up to the GM. But you can choose either 5x5 feet or 1x1 meter if you cannot decide. 5 feet is actually 1.5 meters, but I don't think it matters in actual play.

In other news I've just uploaded the current state of this system. I have simplified the system and made it gridless by default (but you can still use a grid if you want, just homebrew a default movement speed).
If you prefer the old system you can still use it and I will happily answer any questions you have regarding it or the new system.