(Note: While technically it fits in 20mm, many electricians prefer 25mm for 3x TPS to reduce pulling friction. A "Pro" feature would be adding a Friction Factor).
In Australia, the common rule for standard installations (2 cables or more) is that the total cross-sectional area of the cables must not exceed of the internal cross-sectional area of the conduit. conduit size for cable australia
These are for short, straight runs (under 10m, minimal bends). For long runs or multiple 90° bends, drop one size. (Note: While technically it fits in 20mm, many