What is the game object measurement unit?

Questions & Answers
1

I added a plane and a cube the scene both with the same size (10,10,10)

The plane is at least 10 times bigger than the cube! This makes very hard to make correct proportions

Should not the 10 means the same for a plane or a cube?

2

What you see is not the actual size but the SCALE of the object.

3

Yep, change the scale to equal values in both objects…