How 3D models use VRAM?

Im new to 3D modeling, and i wonder how can i measure how much VRAM a model will use when in use. On disk those usually weight several kilobytes, but i think inside they weight much more. How do i find out how much a model weights?

They use it pretty much the same way, by storing list of vertices, their positions, faces, UVs etc, but generally in a more efficient way. You can see total memory, allocated for meshes using stat Memory.