Rotterdam is about 12 times smaller than Melbourne.

Melbourne (the 27 councils of metropolitan Melbourne, without the Yarra Ranges, Cardinia, Mornington Peninsula and Nillumbik) is approximately 3,915 sq km, while Rotterdam (map shows its 22 named neighbourhoods; the area covers the whole city) is approximately 319 sq km, making Rotterdam 8.16% the size of Melbourne.
Tip: This to-scale comparison of Melbourne vs. Rotterdam 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.