With stock springs service manual reads;
Capacity (each leg): 521ml = 17.6US oz = 18.3Imp oz
With inner tube vertical and fully compressed and spring removed oil level should be 97mm (3.8 inch) from the top.
Aftermarket springs may be thicker and displace more oil, check installation instructions that came with the springs. I think progressive recommends 5.5 inches maximum oil level.