This can be a trick question depending on the size of your pool, how much debris you get, and the type of your pool (i.e., indoor vs outdoor, in-ground vs above ground).
Normally, the right number of chlorine tablets depends on the number of gallons of water in your pool. As a rule of thumb, it is ideal to add one tablet for every 5000 gallons.
One thing you need to make sure is to round off the number of gallons to the next 5000. For example, if your pool contains 15,000 gallons of water, consider adding 3 tablets. Likewise, if your pool is 20000 gallons, you will need to add four tablets. If your pool is 16000 gallons, you need to add four tablets. The Doheny's chlorine tablets, for example, are 5 lbs, 55 x 8 oz. individually wrapped tablets.