Terrain exact measure

Hello, I'm new to some things on Unity. Currently working on terrains.

My question is, if I have a completely flat terrain and I want to achieve a perfect 1x1x1 deformation on my terrain, how can I make that?

I have a square brush set to 1x1 size. To get it to 1 of height I know I can set the limit to 1, so once I raise the terrain, the height is set to 1. However to get the terrain to that size I have to move my mouse slightly, making it to be a 1.2x1.3x1 cube

Any ideas? Sorry if not clear