Depends on the weed and what time of the day I start smoking. Sometimes I have work at 6am and ill start smoking at 5:45 am..and ill probably smoke like 3 bowls out of the bong then..
..then smoke again at 11am..then again at 3pm on until bed time. Those days it progessively takes me a lot more to get stoned.

..but sometimes I won't smoke until nighttime...then it doesn't take me as much.

It really depends on alot of stuff. I'd say though I need at least 3 bowls...