As Jamie Mottran astutely pointed out over at Mr. Irrelevant, the numbers add up, and make you think that theoretically, Javale McGee should be able to dunk on a 12 foot rim. Not that you need numbers to figure that out, after watching a dunk like this. McGee threw this one down in Wednesday's Wizards loss to the Bucks.
According to McGee's draft combine numbers, his standing reach is 9'6.5", and his vertical is 32.5". Add those together, and you get 12'3". That's just barely enough to consider the possibility of dunking on a 12 foot rim.
It's only actually been done once before that we know of. Dwight Howard wants to try it, and I think he might be able to pull it off, but the NBA keeps saying no. The one successful try was this dunk, by Michael Wilson of the Harlem Globetrotters. Check it out:
Javale McGee Can Dunk On A 12 Foot Rim [Mr. Irrelevant]