IMO learning to use Shape3d is very, very handy for getting a sense of volume & what affects it. It’s a free DL here: https://www.shape3d.com/Products/Shape3dLite.aspx
I found it easier to learn to use than AKU Shaper, though others have told me they found AKU easier (no idea why, but Shape3d was more like using a classic graphics program, at least to me, right away).
I still use it for many boards, and when “stubbing out” existing designs to make them shorter/wider/thicker for myself and trying to hit a target volume I’ll let the program make the changes, and then handshape from the numbers I get from the tweaked Shape3d file. Results are usually very good. For some reason, when I actually order Marko with CNC cuts from the Shape3d file, rockers seem to come out a bit weird. That weird Marko result could be my fault, but I use the same numbers and put them in by hand when following the process I just described with consistently better results.
Working with slices will really show you how foil and width and thickness changes affect volume because you get an immediate numerical volume result, onscreen, with every change you make.
Eventually (for me, around board 55 0r 60) you start to get an inherent eye for volume. No doubt for some that could happen sooner or later than in my case.
Funny story about volume (not sure if I’ve related it here before): I know a very established shaper here in town who is very generous with his insight. I ran into him one time when I was making a board for a 100 lb intermediate female rider – HPSB semi-step, based on a 7-9 Pearson twin – and was puzzled with what volume and dims to go with, but I came up with about 22-23L. She asked me for 6-0, I think. I made a file for the original 7-9, shrunk it down to 6-0 and tweaked the dims to hit the volume target. When I saw the expert shaper, I asked him what volume he thought I should try to hit, gave him the rider’s details. He said, “Wellll, I don’t really do volume. What’s the length?”
I told him the length.
“So, what width were you thinking?”
Before I could answer, he shot out a width. It was exactly the same as what I had come up with. I told him so.
“So then what thickness?”
And the same thing happened: he shot out a thickness before I could answer, and it was exactly the same (to a 16th") as the thickness I had gotten via starting with volume in Shape3d.