If you want pixel-perfect accuracy, then it should be 2199 x 2199 (you start with one poly, so the first subdiv makes two, and so on).
It may not be necessary to go that high, though, depending on your geometry. If you don't have any details that need to resolve to a single pixel, you might be able to reduce the subdivs without affecting quality too much. I usually set it to the highest value necessary, then reduce it until I start to see artifacts, then raise it a little higher than that.