Mithril ore, like all other mined rocks, respawns at a rate directly proportional to the number of people in the rock's RuneScapeworld. If the world is empty, the ore respawns in 4 minutes; if it is full (with 2000 players), it respawns in 2 minutes. Thus the respawn rate of mithril ore is
where x is the number of players in the world
A table of respawn rates is given below.
A common way to overcome the slow respawn rate of mithril ore is world switching.
This is done by mining the ore on a world until you have mined all the rocks and then logging out to the lobby and switching to a different world. Repeat until the player's inventory is full.