Correct texture size

Well, I’m currently busy with a project (a map) and a friend of mine would like to make the textures.
So imagine we would have a wall in hammer, 128 by 128 units, and the texture was exactly going to be that size, how could I tell photoshop to make the size 128 by 128 valve units?

Perhaps there’s a way to convert valve units to pixels?

You can scale the textures in Valve Hammer, if i remember correctly. Heck, you can make a 1024x1024 texture take up only 128x128 hammer units.

The best resolution for textures is 4x4 px per hammer unit, which is 1024^2 per 128^2 units.