It takes Earth about 365 days to revolve around the Sun once. The more precise orbital period is approximately 365.2422 days, which is why the calendar needs leap years.
That extra fraction of a day accumulates over time. In the Gregorian calendar, an additional day is usually added to February every four years, creating February 29. The century rule makes the system more accurate: years divisible by 100 are not leap years unless they are also divisible by 400.
Earth’s orbit is slightly elliptical rather than a perfect circle. Its average distance from the Sun is about 150 million kilometres (93 million miles), and its orbital speed averages roughly 29.8 km/s. Earth moves somewhat faster when it is closer to the Sun and slower when it is farther away.
“365 days” is the standard rounded quiz answer. Astronomers distinguish among several kinds of year, including the tropical year used for seasons and the sidereal year measured against distant stars.