Now IF I were in europe [>:], and one quart would be one liter, I would add 10cc (1%, or 1/3 Oz) of oil for every % oil increase, and forget about the slight increase in volume that might offset the exact %.
Hey, there is no midget in that engine measuring the exact oil content, and the engine does not notice these small deviations
to go from 17% to 20% would thus requires about 1 Oz/quart, which is close enough to the exact calculations of the previous posters.
I cannot help but be amused by the Imperial measurements. USA was supposed to go metric by 1967! What happened to you guys?