The minimum copper conductor for a socket‑outlet circuit is 2.5 mm². The tool reads it from AS/NZS 3000:2018 Table 3.3. It is a floor, not a design: the current, the voltage drop and the loop impedance can each call for a larger size.
The exceptions
Table 3.3 carries two exceptions. Exception 1 can allow a smaller socket‑outlet conductor, but it sets conditions you must meet first. Read them in the standard before you use a smaller size.
Next step
Size the circuit itself with the cable size calculator. For a typical power point circuit it also selects 2.5 mm².
See also: What size cable for power points in NZ? and Minimum cable size for a lighting circuit.