I'm going to modeling a my computer's mouse But I do not know how to measure the actual size in the blender The problem is that I do not know how to measure the arc

I want to finally print it on a 3D printer
I'm going to modeling a my computer's mouse But I do not know how to measure the actual size in the blender The problem is that I do not know how to measure the arc

I want to finally print it on a 3D printer