In a collection of about 50000 professional games the number of moves ranged from 38 to 411. The distribution is bimodal, with the two tops corresponding to games that were resigned, and that were played out. The average length of a game was 211 moves, that of a resigned game 186 moves, that of a game that was finished and counted 257 moves.
The shortest game lasted for 38 moves, the longest one took 411.