How big is a culture bomb?

Ghandi (the cheeky bastard) just culture bombed my border near his capital, securing several important resources. However, I wasn't watching at the time and so am unsure how many culture bombs he used or how many tiles he grabbed.

I'd like to reclaim some of my resources, but I also want to use my bombs as effectively as possible. How many tiles can a culture bomb capture?

A culture bomb will take all the tiles surrounding the tile bombed:

In other words, if you bomb the green tile, all the red ones would be taken. However, the bombed tile must be either owned by you or neutral and adjacent to a tile owned by you.

According to the official Civ 5 wiki:

A Great Artist can "Culture Bomb" any tile inside or adjacent to your territory. That tile and all six surrounding it immediately become your territory.