Great Falls is located at 38°59'52" North, 77°17'18" West (38.997778, -77.288611).
According to the United States Census Bureau, the city has a total area of 17.91 mi2 (46.38 km2). 17.87 mi2 (46.27 km2) of it is land and 0.04 mi2 (0.11 km2) of it is covered by water. The total area is 0.23% water.
Great Falls is located in the Eastern Standard Time (EST) timezone, GMT-05:00. It observes Daylight Saving Time (DST).