Rule of 20
The Rule of 20 is a guideline for determining if a hand is strong enough to open the bidding. It attempts to refine traditional high card point count by also taking suit length into consideration. The rule is pretty simple: add your high card points plus the number of cards in your two longest suits. If the total is 20 or more, then the hand is worth an opening bid.
Examples
T8 
KT973 
6 
AK865 10 HCP + 5 hearts + 5 clubs = 20. Open 1
in accordance with the Rule of 20.
AQ9 AJ63 JT2 754 12 HCP + 4 hearts + 3 of any other suit = 19. Pass.