What is the average length of a game of chess? I hope this is an appropriate question for this site as I've been wanting a reputable answer. Of course the length of games can vary wildly, but what is the expected number of moves until either a checkmate or trivial draw position is reached? Preferably the answer will be backed by some evidence and is not just "40 moves" like every other internet source.
EDIT: I opened Mega Database 2012 and found there were 515539 games ranging from the 1400s to 2011. As I couldn't find an efficient way to parse the data, I just used the median move value (I hope it's normally distributed. It's probably not though as the largest number of moves was 277... oh well). The median value was 37 moves, but I'm sure that it's a right-skewed distribution given the max value. If I had to hazard a guess to the average value, I'd put it slightly greater than 40 :)

In addition, keep in mind that these are all recorded games. This means that their origin can be from tournaments, matches, or even online competitions. Indeed, the 277 move game was played in a tournament on the Internet Chess Club.



Oddly enough, I found that the average length of a game (played by humans) is roughly 40 moves. Based on the statistics provided by the Chessgames database (685,801) games, the average number of moves is 40.04. Chessgames tends to only include player games of a high caliber, so this doesn't really take into account amateur tournaments. As these games are played by humans, few of them tend to end in checkmate but rather a draw by mutual agreement or a resignation in a lost position.

This may not be the best source, but I've played in over 320 tournaments in my life and many of these games are imported into my personal database. The average number of moves per game is around 38.

I do not have access to my Mega Database 2012 (a database provided by Chessbase) at the moment, but I will post the average number of moves of approximately 5 million historical games when I open it.