Sydney Kingsford Smith International Airport to Portland International Jetport
Approx. 16304 km - about 18h 12m in the air and 19h 30m total from gate to gate, at an average speed around 896 km/h.
Real-world flights on routes this long almost always include at least one stop. Use this nonstop estimate as a guide, and allow extra time for connections and layovers when planning your trip.