lazy man's percentage calculations?

[snowlarbear]

i've read in various places that an easy, though not exact, way to calculate catching an out after the flop is to take your outs and mulitply them by 4.

are there other such shortcuts that anyone uses to do some quick math?

[McSock]

Outs on the river Outs * 2 +2. ex. 6outs 6*2+2 = 14. Very close to 14%

[Slacker13]

Flop
1-8 outs x 4
9-12 outs x4 -1
13-16 outs x4 -4

Turn
1-16 outs x2 +2
17 - 21 outs x2 +3

[snowlarbear]

ah, thanks all.. is this the etymology behind "2+2" publishing?

[IRV]

Someone correct me if I'm wrong, but isn't it 2% for every out + 2. So if you have 9 outs on flop it's 18%+2%=20% and roughly half of that after the turn.

Is this not correct??