There seems to be a lot of different opinions on this. John Palmer says 3 to 4 volumes while BJCP says 2.5 to 2.9 for it.
If you are going for competition stay within those guidelines. Otherwise i would just carb at 12 for a week and see how you like it, if it needs more bring it up 2 or 3 psi and keep bringing it up until you hit the right carb level.
17 to 18 psi does seem to be the general consensus from homebrewers around here however.
Future Brews Graff! - is it beer? is it cider?! is it GOOD?! we will see.
Primary Cherry Apple Wine, White Grape Peach Mango Mead (the mead baby)
Secondary Bog Monster Cranberry Grape Melomel the 2nd
Bottled Bog Monster Cranberry Grape Melomel, Grape Burn and Pillage Pyment
Kegged A Dark Ale w/No Name, Tosh's Cinnamon Challenge Cider, Carabou Slobber