London is about 4.1 times bigger than Birmingham.

Birmingham (map shows its 87 named neighbourhoods; the area covers the whole city) is approximately 381 sq km, while London (including the 32 boroughs of greater London) is approximately 1,572 sq km, making London 313% larger than Birmingham.
Tip: This to-scale comparison of Birmingham vs. London 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.