Source : 1ouk.com
When neither side has any pawns the game must be completed within a certain number of moves or it is declared a draw. When a piece is captured the count starts again from scratch only if it is the last piece of one side in the game.
When neither side has any pawns left mate must be achieved in 64 moves. The one who is in disadvantage will be the one who will do the counting. He or she may stop counting whenever he or she favors. If the disadvantage side checkmates the advantage side and did not stop counting , the game will be declared a draw.