⚠️This fact has been debunked
The number cited (170,000,000,000,000,000,000,000,000 or 1.7 × 10^26) is astronomically incorrect. The actual number of possible chess games after 10 half-moves (5 moves per player) is 69,352,859,712,417 - approximately 69.35 trillion. The fact overstates this by a factor of about 2.5 trillion times. The confusion may stem from mixing up different chess complexity metrics: the Shannon Number (10^120 for complete games) vs opening sequences.
There are 170,000,000,000,000,000,000,000,000 ways to play the ten opening moves in a game of chess.
The Mind-Boggling Math Behind Chess Opening Moves
Think chess is just a simple board game? Think again. After each player makes just their first five moves, there are already 69,352,859,712,417 possible games that could have been played. That's over 69 trillion different ways the opening sequence could unfold.
But here's where many people get confused: various inflated numbers circulate online, including the wildly incorrect claim of 170 septillion possibilities. The truth is impressive enough without the exaggeration.
How Chess Complexity Actually Works
Chess complexity grows at an explosive rate, but in predictable stages. On move one, White has 20 legal moves (16 pawn moves and 4 knight moves). Black then has 20 responses. By move two, there are 400 possible positions. By move three, we're at 8,902 positions.
This exponential growth continues until we reach that 69.35 trillion figure after ten half-moves (or "ply" in chess terminology). A half-move is one player's turn, so ten half-moves equals five complete moves by each player.
The Shannon Number: Where the Real Mind-Blowing Math Lives
The confusion about chess's complexity often stems from mixing up opening sequences with complete games. Mathematician Claude Shannon calculated that the total number of possible chess games is approximately 10^120 - a number so large it's called the Shannon Number in his honor.
To put that in perspective:
- Atoms in the observable universe: approximately 10^80
- Possible complete chess games: approximately 10^120
- That means there are 10^40 times more possible chess games than atoms in the universe
Why This Matters
This astronomical complexity is exactly why chess remains unsolved despite modern supercomputers. Unlike checkers (solved in 2007) or tic-tac-toe (trivially solved), chess's game tree is so vast that brute-force calculation of every possibility remains impossible.
Professional players don't memorize all 69 trillion opening sequences - they understand patterns, principles, and key variations. Even the most extensively studied openings represent just a tiny fraction of what's mathematically possible.
So while 69 trillion may not sound as sexy as 170 septillion, it's the real number. And honestly? It's mind-blowing enough.