about 54 TB. But only about 2% of tiles have ever been seen. Each zoom level has 4 times as many tiles as the previous level and zoom level 18 (the highest) doesnt have a lot of data.
Quote: "OSM does NOT pre-render every tile. Pre-rendering all tiles would use around 54000GB of storage. As the following table shows, the majority of tiles are never viewed. In fact just 1.79% are viewed."
Those figures are about a year old, though it does give a newer figure for space used which is about 1200TB or 2.7% of the total size estimated.
