Sydney is about 9 times bigger than Athens.

Athens (map shows its 34 named neighbourhoods; the area covers the whole city) is approximately 412 sq km, while Sydney (the 30 councils of metropolitan Sydney, without the Blue Mountains, Hawkesbury, Wollondilly and the Central Coast) is approximately 3,810 sq km, making Sydney 825% larger than Athens.
Tip: This to-scale comparison of Athens vs. Sydney uses the Mercator projection, which distorts the size of regions near the poles.
Our free app, MapSize by MyLifeElsewhere — compare any two places, to scale on your mobile device.