Birmingham is about 14 times smaller than Istanbul.

Istanbul is approximately 5,343 sq km, while Birmingham (map shows its 87 named neighbourhoods; the area covers the whole city) is approximately 381 sq km, making Birmingham 7.13% the size of Istanbul.
Tip: This to-scale comparison of Istanbul vs. Birmingham 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.