I would go at this from the other direction (the runway length is clearly fixed so you can only limit your landing weight).
As far as I am aware, there is no standard factor to apply to dry distances as it would depend on a number of factors.
You will need to dive into your AFM and check out the performance section.
For my type, you determine the Dry landing distance required (taking into account the usual approach climb / brake limit etc). Once you have this figure, you then go into a simplified table against the dry distance and read off the contaminated column depending on the conditions (wet, 0.125 / 0.2 / 0.3 / 0.4 / 0.5 inches water depth and so on for slush, snow, wet ice etc).
On the basis of your example, assuming the runway at Vienna is not grooved (and hence treated as dry) then Wet runway would be 9450' if landing at VRef and 10950' if landing at VRef + 10 (without reversers or tailwind and from 50' screen height). Goes to show how important speed control is!
However, we rarely get out the AFM as we have a route performance manual and Flygprestanda showing the max landing weight for each runway and contaminated condition.