Sorry, but there's a lot of wrong information in this thread. FWIW dragonfly has it right. The rule in all situations is that a raise has to be at least the size of the previous bet or raise.
Here's an example that will hopefully clear it up:
- Preflop, blinds are 50/100
- Folded to MP, who wants to raise. He has to make it at least
200 (ie: 100 more than the big blind of 100)
- He decides to make it 300 though, because he's old school and doesn't believe in this minraising nonsense the kids are doing these days. Notice that's a raise of 200
on top of the 100 bet by the big blind.
- It's then folded to the button, who decides that he wants to reraise. He has to make it at least 500
(not 600), because 300 (the size of the bet to him) + 200 (the size of the previous raise) = 500. He makes it 500.
- Everyone else folds because minraises are scary, hand over.
Here's the relevant section of Robert's Rules - you're looking at Rule 6 in particular: http://www.homepokertourney.com/robe...NG_AND_RAISING
For what it's worth, I have
heard of some bar leagues and other games going with a flat "double the previous bet" rule in the name of simplicity and helping people who don't want to do maths (ie: 50/100, someone raises to 200, minimum raise is then to 400, so on) but what I've outlined above is the 'correct' way.