Leap Years to Days (yr (366) to d)
1 leap year equals 366 days exactly.
How to convert leap years to days
To convert leap years to days, multiply the number of leap years by 366. This factor is exact. To go the other way, multiply days by 0.002732240437 (rounded).
days = leap years × 366
Example: 10 leap years = 3,660 days.
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
Leap Year (yr (366))
A calendar year of exactly 366 days, with the leap day on February 29.
Julius Caesar's edict, effective 1 January 45 BC, turned the Roman calendar into a solar one with an extra day every fourth year. The English phrase is thought to come from weekdays: a fixed date normally moves ahead one weekday each year, but after a leap day it moves two, appearing to leap over one. The extra day is 29 February, used since about the fifteenth century, and British law recognized it formally in 1750.
A leap year has 366 days, or 31,622,400 seconds. The Gregorian rule, which now governs most of the world, makes a year a leap year when divisible by four, except century years that are not divisible by 400. So 2000 was a leap year and 1900 was not. That leaves 97 leap years in each 400-year cycle and a mean year of 365.2425 days, close to the tropical year.
1 leap year = 31,622,400 seconds (exactly).
Sources: Wikipedia: Leap year; Wikipedia: Common year
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
Related conversions
- Days to leap years (reverse)
- Leap years to seconds
- Leap years to minutes
- Leap years to hours
- Leap years to weeks
- Leap years to months
- Leap years to years
- Seconds to days
- Minutes to days
- Hours to days
- Weeks to days
- Months to days
- Years to days
- Milliseconds to days
- Microseconds to days
- Nanoseconds to days
- Decades to days
- Centuries to days
- Millennia to days
See all time units.