Rotterdam is about 11 times smaller than Karachi.

Karachi is approximately 3,527 sq km, while Rotterdam (map shows its 22 named neighbourhoods; the area covers the whole city) is approximately 319 sq km, making Rotterdam 9.05% the size of Karachi.
Tip: This to-scale comparison of Karachi 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.