There are approximately 365.25 days in a normal year. This measurement represents one Julian year, which is a recognized astronomical unit of measurement.
A year is measured by how long it takes the Earth to orbit the sun. The exact number of days is 365.2422 days, which is rounded to 365.25. The calendar is kept in sync with seasonal shifts by shortening the number of days in the normal year to 365. The quarter days are put together and added to the calendar once every four years, which accounts for the custom of leap year.
The Julian year is not one of the fundamental units recognized by the International System of Units (SI) but is utilized by International Astronomical Union (IAU) as a unit of astronomical measurement.