Istanbul is about 4.2 times bigger than Rome.

Rome is approximately 1,287 sq km, while Istanbul is approximately 5,343 sq km, making Istanbul 315% larger than Rome.
Tip: This to-scale comparison of Rome vs. Istanbul 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.