The rank of each card used in Texas Hold'em when forming a five-card high poker hand, in order of highest to lowest rank, shall be: ace, king, queen, jack, 10, 9, 8, 7, 6, 5, 4, 3, and 2. All suits shall be considered equal in rank. The ace would be considered low any time the ace begins a straight or a straight flush.
Under high rules, an ace can rank either high (as in A. K&c Q&c J. 10&`, an ace-high straight) or low (as in 5&c 4. 3&e 2&e A&`, a five-high straight), but cannot simultaneously rank both high and low (so Q&` K&` A&c 2&e 3.