The Ball shall weigh not less than 5 1/2 ounces, nor more than 5 3/4 ounces. It shall measure not less than 8 13/16 inches, nor more than 9 inches in circumference. Subject to agreement to the contrary, either Captain may demand a new ball at the start of each innings. In the event of a ball being lost or becoming unfit for play, the Umpires shall allow another ball to be taken into use. They shall inform the Batsmen whenever a ball is to be changed.

NOTES ON LAW 5

1. All cricket balls used in First-class matches should be approved before the start of a match by the umpires and captains. The latter may demand a new ball at the start of each innings.
2. Except in the United Kingdom, or if local regulations provide otherwise, after 200 runs have been made off a ball in First-class matches, the captain of the fielding side may demand a new one. In First-class matches in the United Kingdom the fielding side may demand a new ball after 85 (6 ball) overs have been bowled with the old one. In other grades of cricket these regulations will not apply unless agreed before the toss for innings. [see original]
3. Any ball substituted for one lost or becoming unfit for play should have had similar wear or use as that of the one discarded.