Odds Based on Hand Matchups

Favorite-to-underdog matchup	Probability	Odds For
Pair vs. 2 undercards	0.83	4.9 : 1
Pair vs. lower pair	0.82	4.5 : 1
Pair vs. 1 overcard, 1 undercard	0.71	2.5 : 1
2 overcards vs. 2 undercards	0.63	1.7 : 1
Pair vs. 2 overcards	0.55	1.2 : 1

Head-to-Head Starting Hand Matchups

When comparing two starting hands, the head-to-head probability describes the likelihood of one hand beating the other after all of the cards have come out. Head-to-head probabilities vary slightly for each particular distinct starting hand matchup, but the approximate average probabilities, as given by Dan Harrington in Harrington on Hold'em [p. 125], are summarized in the following table.

This chart is provided courtesy of Wikipedia and is available under the Creative Commons Attribution-ShareAlike License.