Allis also estimated the game-tree complexity to be at least 10123, based on an average branching factor of 35 and an average game length of 80. As a comparison, the number of atoms in the observable universe, to which it is often compared, is estimated to be between 4×1079 and 4×1081.
https://en.wikipedia.org/wiki/Shannon_number
The Shannon number, named after Claude Shannon, is a conservative lower bound (not an estimate) of the game-tree complexity of chess of 10120, based on an average of about 103 possibilities for a pair of moves consisting of a move for White followed by one for Black, and a typical game lasting about 40 such pairs of moves.
https://en.wikipedia.org/wiki/Shannon_number
FYI: How Many Different Ways Can a Chess Game Unfold? Almost nothing looks more orderly than chess pieces before a match starts. The first move, however, begins a spiral into chaos. After both players move, 400 possible board setups exist. After the second pair of turns, there are 197,742 possible games, and after three moves, 121 million. At every turn, players chart a progressively more distinctive path, and each game evolves into one that has probably never been played before.
http://www.popsci.com/science/article/2010-12/fyi-how-many-different-ways-can-chess-game-unfold
This is how a computer looks at chess. It thinks about it in a world of all possible moves, and it makes a big tree for all of those moves, like this: In this tree, there are 20 possible moves for white. There are 20 * 20 = 400 possible moves for black, depending on what white does.
http://electronics.howstuffworks.com/chess1.htm
This includes some illegal positions (e.g., pawns on the first rank, both kings in check) and excludes legal positions following captures and promotions. Taking these into account, Victor Allis calculated an upper bound of 5×1052 for the number of positions, and estimated the true number to be about 1050.
https://en.wikipedia.org/wiki/Shannon_number
Now white can move again. This next move depends on the first move that white chose to make, but there are about 20 or so moves white can make given the current board position, and then black has 20 or so moves it can make, and so on. This is how a computer looks at chess. In this tree, there are 20 possible moves for white. There are 20 * 20 = 400 possible moves for black, depending on what white does. Then there are 400 * 20 = 8,000 for white.
http://electronics.howstuffworks.com/chess1.htm
The number of possible chess positions after White’s first ply move is 20 (16 pawn moves and 4 knight moves). There are 400 possible chess positions after two ply moves (first ply move for White followed by first ply move for Black). There are 5,362 possible positions (White’s second ply move) or 8,902 total positions after two ply moves each. There are 71,852 possible positions or 197,742 total positions after four moves. There are 809,896 possible positions or 4,897,256 total positions after 5 moves.There are 9,132,484 total positions after 6 moves. From move 7 the possible positions stabilize as chess lines end, even from move 2 some chess lines end. There are +-10,921,506 total possible positions after 7 moves.
https://www.chess.com/chessopedia/view/mathematics-and-chess
(This influential paper introduced the field of computer chess.) Shannon also estimated the number of possible positions, of the general order of 64 ! 32 ! 8 ! 2 2 ! 6 {\displaystyle \scriptstyle {\frac {64!}{32!{8!}^{2}{2!}^{6}}}} , or roughly 1043.
https://en.wikipedia.org/wiki/Shannon_number
There are a total of 20 opening moves that can be played at the start of a chess game. E…ach pawn has a possibility of moving either one or two steps forward creating 16 possible first moves with a pawn. Both knights have two squares they can move to creating another 4 possible opening moves.
http://www.answers.com/Q/How_many_possible_first_moves_are_there_in_chess
There are 20 possible opening moves in chess. There are eight pawns and each pawn has two possible moves. There are two knights and each knight has two possible moves. There are 20 possible opening moves in chess. There are eight pawns and each pawn has two possible moves. There are two knights and each knight has two possible moves.
http://www.answers.com/Q/How_many_possible_first_moves_are_there_in_chess
how many possible moves in chess
The game-tree complexity of chess of 10120, based on an average of about 103 possibilities for a pair of moves consisting of a move for White followed by one for Black, and a typical game lasting about 40 such pairs of moves. In chess, there are an average of about 103 possibilities for a pair of moves consisting of a move for White followed by one for Black, and a typical game lasting about 40 such pairs of moves.