How many hits until an iron pick will break in minecraft?

An iron pick has a durability of 251. If you want to find out any of your tool's durability, press f3 + h (doesn't have to be at the same time, you could hold f3 then press h) then open your inventory and hover your mouse over the tool you wish to see the durability of. The first number (i.e. x/251 if iron tool) will be your current durability.