The amount of sprinklers recommended for each irrigation zone will depend on the flow rate of your home's water supply, which is measured in gallons per minute. Once you've decided how many sprinkler heads you plan to use in all zones, compile a total figure for all the flow rates of all the sprinkler heads combined. Divide this figure by the flow rate of your water supply. The result indicates how many zones you need, and how many sprinklers you need in each zone. For example, if you have nine sprinklers and you've determined that three zones are needed, this means you need three sprinklers for each zone.