I've just started adding dimensions to my plan, and I've noticed that the dimensions of each wall don't match the wall lengths I entered!

For example, I have one "sticking out" wall that has a length of 126, but the dimension from corner to corner measures 128.

On the other hand the opposite wall has a length of 196 and the dimension, corner to corner, reads 193.

It seems to be the thickness of the walls that is the problem. I had assumed that the wall lengths I was entering would correspond to the interior measurements I made - after all, I can't measure the outside of the room.

The sizes need to be exact because I want to plan a kitchen.

Any ideas how I should proceed?