Rotterdam is about 51 times smaller than Beijing.

Beijing is approximately 16,411 sq km, while Rotterdam (map shows its 22 named neighbourhoods; the area covers the whole city) is approximately 319 sq km, making Rotterdam 1.95% the size of Beijing.
Tip: This to-scale comparison of Beijing 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.