Days to Common Years (d to yr (365))
1 day equals 0.002739726027 common years (rounded).
How to convert days to common years
To convert days to common years, multiply the number of days by 0.002739726027. The factor is rounded to 10 significant digits. To go the other way, multiply common years by 365.
common years = days × 0.002739726027
Example: 10 days = 0.02739726027 common years.
Months and years are not constant. This site uses the average Gregorian year of 365.2425 days, so one 'year' converts to 365.2425 days, not 365; use 'common year' for exactly 365 days.
About these units
Day (d)
24 hours or 86,400 seconds. The mean solar day; the actual rotation of the Earth is about 4 minutes shorter (see sidereal day).
Old English dæg is the root of our day, with close cousins in German Tag, Dutch dag and Icelandic dagur, all descending from Proto-Germanic dagaz. It is the oldest unit here, because the cycle of light and dark needs no instrument. Yet the day we count is a constructed average: the actual interval from one noon to the next varies through the year by up to about 7.9 seconds, because Earth's orbit is elliptical and its axis is tilted.
Astronomers smooth this out with a fictitious mean Sun, giving the mean solar day, and the day in the SI sense is fixed at exactly 86,400 seconds. Reality has drifted slightly: the mean solar day has recently averaged about 86,400.002 seconds, and tidal drag from the Moon is lengthening it by about 2 milliseconds per century. That is why 27 leap seconds were added to UTC between 1972 and 2022. One rotation measured against the distant stars is shorter, about 23 hours 56 minutes 4.09 seconds, and a year contains one more of these sidereal days than solar days.
1 day = 86,400 seconds (exactly).
Sources: Wikipedia: Day; BIPM: SI Brochure, 9th edition
Common Year (yr (365))
A calendar year of exactly 365 days, without a leap day.
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.
1 common year = 31,536,000 seconds (exactly).
Sources: Wikipedia: Common year; NIST SP 811 Appendix B.8: factors for units outside the SI
Related conversions
- Common years to days (reverse)
- Days to seconds
- Days to minutes
- Days to hours
- Days to weeks
- Days to months
- Days to years
- Days to milliseconds
- Days to microseconds
- Days to nanoseconds
- Days to decades
- Days to centuries
- Days to millennia
- Seconds to common years
- Minutes to common years
- Hours to common years
- Weeks to common years
- Months to common years
- Years to common years
See all time units.