Similar to the Rule of 15, the Rule of 20 is a bridge bidding convention that is used to help decide if your hand is suitable for opening the bidding in a game of bridge. The Rule of 20 is used by any of the first three players (the fourth player can use the rule of fifteen instead)
Generally a player will open the bidding if their hand contains 12+ points and pass if their hand contains fewer points. Sometimes, though, you might be tempted to open the bidding with a hand containing fewer than 12 points. You need a way of deciding if this is sensible option and this is where the Rule of 20 comes in.
The Rule of 20
Add the number of High Card Points in your hand to the length of your longest two suits. If teh total is 20+ you have satisfied the Rule of 20 can open the bidding if you want to.
Take a look at these examples
Our hand has eleven points. If we add this to the length of our two longest suits we get a total of 20, so we can open the bidding if we want to.
This is a tempting looking hand. It has honours in every suit. Can we open the bidding? It contains 11 points, but if we add that to the length of our longest two suits we get a total of just 19. This doesn’t satisfy the Rule of 20 so we must pass.