First: Count the number of potted plants, both hanging and standing.
Second: Determine the route the tube will need to run to be generally out of sight from the garden hose faucet all the way to the furthest plant in the system. Make sure to include enough slack to be able to run the tube out of sight. A straight connector is needed to connect lengths of tube together if needed. This is the main “header”.
Then: measure the lengths of tube needed to tee off the header to supply each plant along the route of the header. Remember to allow enough length to run the tube generally out of sight.
A typical 6 pack is provided with 7 Tee’s (the last plant won’t need one, so that means two spare), plus two straight connectors. Any additional tube purchased will come with extra straight connectors. If a length of tube is cut too short a straight connector will be needed to add more length.