How do I change the Unit size for a project?

From what I’ve read, Unity defaults to 1 unit = 1 meter. This sounds good to me, but I’d like to verify that the project I’m working on is indeed setup this way. I can the the gravity setting is currently set to -40 instead of -9.1 which makes me think that the project scale is set to something else. Is there a “Unit Size” setting somewhere? A lot of people have been saying that unit size does not matter as long ass everything is scaled together properly but I’m not sure. From what I can tell, gravity, the speed of sound and some other things will be affected. I can’t find a Unit setting in the project settings, is it perhaps a unity pro setting only?

If you create a default cube in your scene, it will be set up as a 1m cube. If what you are concerned about is making sure that objects that you import in are at the proper scale, just set up a scene in your 3D platform, create a 1m cube in it, and then make sure that the cube you import from your 3D platform is the same size as the default cube in Unity.
The other thing to keep in mind is that size does matter when it comes to physics. My advice would be to always work in real world units (1 unity unit = 1 meter). Might not matter in some projects, but it is just a good habit to get into… and as you build your own asset library it will make things much easier!

A unit is a unit, so there’s nothing else to set it to. Units are arbitrary, and only mean what you say they mean. If you put gravity at -9.81, then that means units are meters as far as physics goes, as long as you assume Earth-normal gravity. If you use 343 for the speed of sound in the audio settings, that means 343 units per second.

Wrong to say it is arbitrary. The default cube is one meter. Because the default unit is 1 meter. There is no program where the units are arbitrary. That is absolutely false. All units have to mean something internally. Not just physics simulation. But Lighting also works on real world scale. All of the math in a program has to be calculated so that a Unit means something. From there you can assign an arbitrary value to a unit. But that is you making that assignment. It is not arbitrary by default.

The one-meter means a lot now in VR, and AR. These applications use real-world distances so you have a perfect depth of field.