When will we run out of Grave Plots?

A grave plot takes up roughly 2 square metres. There is 148,940,000 square kilometres of land area on Earth. That's enough for 74 trillion people. And that's just burying them one to a plot. Realistically you could bury them three or four deep. But then realistically there's plenty of land not suitable for burials.

Still, we've got an awful lot of space left. And if it really becomes a serious issue, we will just move to cremation or whatever.