For a dished head of inside diameter (D), inside crown radius (rc) and inside knuckle radius (rk), you'll be able to calculate the inside height (h) using plain mathematical formulas.
h = rc - {[(rc - rk)^2 - (0.5xD - rk)^2]^0.5}
The inside volume of a dished head consist of two parts:
a) The volume of a spherical sector whose radius is equal
to rc less the volume of a right circular cone of radius
(0.5xD - rk) and a height of (rc - h).
b) The volume derived by revolving a circular sector whose
radius is equal to rk about the longitudinal axis of
the dished head. The radius of revolution is equal to
the horizontal distance from the centroid of the
circular sector to the longitudinal axis.
If you agree with the above analysis, then there might not
be a straight forward formula to get the volume of a
dished head particularly on cases where the inside depth
where you want the volume taken is less than the calculated inside height of the dished head (as per formula shown above).