The Prime Meridian (0° longitude) runs through Greenwich, London. Istanbul straddles Europe and Asia at approximately 29° East longitude.
The often-cited "2,000 km / 1,200 miles" uses equatorial degree length (111 km), which overestimates east-west distance at higher latitudes. The accurate surface distance along the 41st parallel is ~2,440 km.
For context: Istanbul is roughly as far east of Greenwich as Moscow is north of the equator.