Stack people when?

As in, how many more chips should you have than someone else when you will put them all-in automatically if you bet at them?

3x? 4? 8?

It depends

{EDIT: OK I'll expand a bit}
It sounds like you are talking about calling an all-in, which is different than raising someone all-in. Generally people say call an all-in with any hand if you have 10x their stack. I think Harrington mentioned 8x was his cut-off.

You need to be more specific about your request. If I have an equal stack and our M is 100 then I'm going to want AA, KK to raise them all-in. If I'm twice their stack with an M of 6, K6 might look appealing.

Another thing to consider is the BB stack size. Suppose you're on the button with AT and the BB has 7 BB, if you raise to 3BB are you going to fold if he pushes? Of course not, so I just raise to 7BB and make a race out of it.

I have a feeling you read the thread I wrote earlier...