Use the priming sugar calculator here
http://www.northernbrewer.com/priming-sugar-calculator/
It lets you adjust volume, as well as sugar (if you wanted to use something other than dextrose/corn sugar) and CO2 volumes based on style, and temp also (I heard someone else say use the highest temp that the beer rose to during fermentation - but there it says CURRENT temp of beer - so not exactly sure on that one... I just use current as it says). Also it gives you the amount in both weight and cups, so you dont have to weigh out (or look up) a particular sugar to figure out its volume equivalent, which saves some time doing calculations (I used it the other day just for this feature - i had a 5 gal recipe that called for 2 lbs brown sugar, and i needed to convert to cups for a 1 gal batch). Quite a nice tool to have... Bookmark the page!