Rule of 20

Add the number of cards in the two longest suits to the number of points held.

If the result is 20 or greater the hand is worth an opening bid.

The Rule of Twenty Six  (Courtesy of Harold Schogger)

If your partner makes a splinter bid and you add up all your points outside the splinter suit and if it comes to 26 or more you should consider bidding a slam.

For example:

                                  WEST             EAST

SPADES                    AK873             QJ65

HEARTS                    43                   AK652

DIAMONDS               AQ65               K83

CLUBS                      62                    9        

BID                             1 SPADE       4 CLUBS

Then West should immediately add his points outside the splinter suit to a known guarantee of 13-15 points. Since his points total 14 and his partner is promising 13-15, then he knows the total is 26 and he should immediately be interested in a slam as 6 Spades is an easy make. West should therefore make suitable overtures either by cue bidding or Ace asking.

But if the hands are as follows:

                                  WEST             EAST

SPADES                    AK873             QJ65

HEARTS                    43                    AK652

DIAMONDS               Q2                    K83

CLUBS                      KQ62                9  

BID                           1 SPADE          4 CLUBS

The points you have outside the splinter suit are now 9 and added to the guaranteed 13, totals only 22.    So although you have 27 points between the two hands, a slam is impossible and game only is the contract.