How to get the actual terrain size (X, Y, Z) in a script?

Hi, how can I get exactly the terrain size? Using workspace.Terrain.Size gives inconsistent information.

As you can see in the following images, I have created a very little and simple terrain, using Terrain Editor, with X=100, Y=4, Z=100 but when I get the terrain size from a server script (I put it directly in the workspace) using workspace.Terrain.Size I get non sense information:

How can I get, in a server script, the exact terrain size?

Thanks and bye