I want to calculate the volume of a model.

The area indication is good. But I believe the volume should be the same as the area since I have extruded the face with 1m.

Does anybody have an idea why? Maybe because it is not one face (they are one object in object mode)

[![enter image description here][1]][1]

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/wiT91VSY.jpg
  [2]: https://i.sstatic.net/GD9ZXhQE.jpg