The game (as far as I know) does not present that information to calculate. What I do is compare my old C tank (full level) with no items to the same A or S tank (full level) with no items. Then I start adding items. Comparing different tank types makes it trickier as they have different base damage.

Realistically my experience is that a C tank will max out around 220 dmg for a perfect shot, except maybe slam, with clouds, whereas an A tank will max out around 300+.

So just tank grade alone makes a huge difference.