How many XP orbs are needed to restore 1 durability point?

Assuming that you have Mending, one XP orb restores 2 durability points. A simple way to mend a tool without using dual wielding requires a manual gold farm. You hold the item that needs to be repaired, and hit the pigmen with the item. Though it consumes durability, more durability will be restored than taken. I hope this helps.