Istanbul is about 2.8 times bigger than Jacksonville.

Jacksonville (map shows its 197 named neighbourhoods; the area covers the whole city) is approximately 1,935 sq km, while Istanbul is approximately 5,343 sq km, making Istanbul 176% larger than Jacksonville.
Tip: This to-scale comparison of Jacksonville 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.