opengl – How do I set the size of a single ‘unit’ in my game?

I’m currently trying to remake/port an old game created on Unreal Engine 2.5 to my own engine, and I have access to its physics data. It’s using a scale of 80 units per meter, or 1 unit = 1.25cm.

The walk speed value for example is 5, and physics is simulated at 60 FPS, so the walking speed I need to implement would be 3.75 meters per second.

But I don’t exactly know what the size of a game engine’s “unit” actually means. I of course want my own engine (I’m using C++, OpenGL, and GLM) to use this same scale, but I’m not sure how to go about that. I’d assume this affects not only physics/movement code, but the scale of models and maps I load in as well, so it’s important to make sure it’s the same as in the original game.

How would I implement this? What parts of a game does the size of a ‘unit’ affect and how? Just the physics and movement calculations, or the graphics side as well (matrices, clipping space, FOV, etc.)?

(I’m not sure if I’m overthinking things)