How far would average sea level rise from a 25% increase in total ocean volume?
It is not hard to do this calculation if you have global topography. Using a version with $\frac{1}{6}$- degree resolution and a sea level rise of 1027 m, the result is @Erik's value of 445 million cubic km. Here's the bit of MATLAB code:
H = 1027;   % sea level rise (m)
topo(topo&lt;0) = 0;   % change all ocean depths to zero
topo(topo&gt;H) = H;   % level off all land at a height of H
topo = topo.*(cosd(lat')*ones(1,2160)); % land volume per grid cell
land = sum(topo(:))*18.5^2/1000; % total land volume in km^3
water = sum(cosd(lat))*2160*18.5^2*H/1000 - land; % added water volume

Greenland and Antarctica fare ok, but Europe and Australia are basically gone: