Common Year (yr (365))

CalendarCurrent unit

A calendar year of exactly 365 days, without a leap day.

1 common year = 31,536,000 seconds (exactly).

About the common year

Calendar makers needed whole numbers of days, so the common year is simply 365 of them, or 31,536,000 seconds at 86,400 seconds per day. It makes up 303 of every 400 years in the Gregorian calendar. Because 365 is 52 weeks plus one day, a common year begins and ends on the same weekday, and each date falls one weekday later than the year before.

The trouble is that the Earth takes about 365.24 days to complete a cycle of seasons, so a common year runs roughly 5 hours, 48 minutes and 46 seconds short of the tropical year. The shortfall adds up to a full day in about four years, which is why leap years exist. NIST lists the 365-day year as an exact conversion, while its tropical and sidereal years are measured quantities that differ in the fifth significant figure.

Sources: Wikipedia: Common year; NIST SP 811 Appendix B.8: factors for units outside the SI

Common Year conversion chart

1 common year expressed in every other time unit:

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