Multiple choice general knowledge which city is used as reference longitude for indian standard time? gaya chennai mirzapur lucknow Reveal answer Fill a bubble to check yourself C Correct answer Explanation The Indian Standard Time is calculated from the longitude of 82.5°E, which passes near Mirzapur in Uttar Pradesh. This reference meridian was chosen to balance time differences across the country's width. The IST is 5 hours 30 minutes ahead of UTC.