Dusseldorf is about 1.9 times smaller than Athens.

Athens (map shows its 34 named neighbourhoods; the area covers the whole city) is approximately 412 sq km, while Dusseldorf is approximately 217 sq km, making Dusseldorf 52.77% the size of Athens.
Tip: This to-scale comparison of Athens vs. Dusseldorf 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.