First of all, it all depends on the area you live in and the amount of signal that is arriving at your location. Go to http://myswitch.digitalready.gov.au/.
On the loading page, just enter your location and then click the red “Get Info” button to find out how much signal you are getting. In a good area where you are picking up 90-100% of signal reception. Usually 5-6 points can be handled at one time.