How to create 3D game object in specified pixel size?

I want to create an game object in some specified size. For example to create an 3d cube in 250x350 pixel size. I am new for unity. If anyone know help me, thank.

You can use Scale parameter of transform. By default cube is 1x1x1 unity unite, Scale is multiplier

On unit in Unity is one meter. Convert meters to inches and create an object with that size. If scale of your Unity objects represents 1 meter to 1 scale unit then you can create object with scale value representing the 1 meter to 1 inch otherwise you have to take scale also into consideration.