Chess by the numbers
What is the longest possible chess game?
Under today’s FIDE rules, 8,848½ moves, by François Labelle’s calculation. The longest game actually played in a tournament lasted 269 moves: Nikolić–Arsović, Belgrade 1989, a draw after more than 20 hours.
Why there is a limit at all
A game used to be able to go on forever: a draw by repetition or by the fifty-move rule had to be claimed by a player, and if nobody claimed it, play went on. Since 2014 the FIDE rules end a game automatically when the same position appears for the fifth time, or after 75 moves by each side without a capture or a pawn move. That makes every game finite.
Where 8,848½ comes from
To keep a game alive under the 75-move rule, someone has to capture or move a pawn at least every 75 moves, and those moves run out. Sixteen pawns can make at most six moves each, 96 in all, and 30 pieces can be captured, which makes 126. But the pawns block each other, and for them to get past one another 8 of the pawn moves must also be captures, which leaves 118. The longest game is therefore 118 stretches of 75 moves, less three half-moves for the times the side making progress has to change:
118 × 75 − 3 × ½ = 8,848½ moves
Under the old fifty-move rule, if every draw had to be claimed as soon as possible, the same reasoning gives 118 × 50 − 1½ = 5,898½ moves.
The longest and shortest real games
Real games are nowhere near the limit. The longest tournament game on record, Ivan Nikolić against Goran Arsović in Belgrade in 1989, lasted 269 moves and more than 20 hours, and ended in a draw. The shortest decisive tournament game, Đorđević against Kovačević at Bela Crkva in 1984, lasted three: 1. d4 Nf6 2. Bg5 c6 3. e3 Qa5+, and White resigned, since the queen’s check also attacks the bishop on g5.
The shortest game the rules allow is shorter still: the Fool’s Mate, checkmate after two moves each.
Questions people ask
Is the number of possible chess games finite?
Yes, under today’s rules. Labelle puts it between about 1029,241 and 1034,082; see how many possible chess games there are.
Does the fifty-move rule still exist?
Yes. After 50 moves by each side without a capture or a pawn move, a player may claim a draw; after 75 such moves the game ends by itself.