Calculate Volume Of 3d Model. V 1 6 dot a cross b c. This way you can count the pixels or even larger pixels as pixel groups to get the volume.
I calculate volume based on same geometry. If you have this you just sum up the volumes of all tetrahedrons. V 1 6 dot a cross b c.
With voxel the model is not described as spacial vertex array they are actually described as collections of tiny pixel of volumes.
With tetrahedrons of the models. Volume mm 3 units. This is easily done using. You can calculate the volume if you create a 3d mesh e g.