Months to Days (mo to d)
1 month equals 30.436875 days exactly.
How to convert months to days
To convert months to days, multiply the number of months by 30.436875. This factor is exact. To go the other way, multiply days by 0.03285488408 (rounded).
days = months × 30.436875
Example: 10 months = 304.36875 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
Month (mo)
One twelfth of an average Gregorian year: 30.436875 days. Calendar months actually range from 28 to 31 days.
Month and Moon are cognates, and the unit began as the Moon's cycle of phases, about 29.53 days from one new moon to the next. The trouble is that 12 of these fall short of a solar year, so calendars have had to choose. The Islamic calendar stays purely lunar, so its year is about 11 days shorter than the solar year, while the Hebrew calendar is lunisolar, using a 19-year cycle with an extra month. Even the start of a lunar month is still debated between observing the crescent and calculating it.
Gregorian months are a compromise that drifted far from the Moon. Their lengths run from 28 to 31 days, and this site uses their mean of 30.436875 days, one twelfth of the average year. The names also keep Roman history: September to December preserve the Latin numerals for seven to ten, since they were originally the seventh to tenth months, and Quintilis and Sextilis were renamed for Julius Caesar and Augustus. When a contract says month, check whether it means a calendar month or thirty days.
1 month = 2,629,746 seconds (exactly).
Sources: Wikipedia: Month; Wikipedia: Lunar calendar
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 months (reverse)
- Months to seconds
- Months to minutes
- Months to hours
- Months to weeks
- Months to years
- Months to milliseconds
- Months to microseconds
- Months to nanoseconds
- Months to decades
- Months to centuries
- Months to millennia
- Months to picoseconds
- Seconds to days
- Minutes to days
- Hours to days
- Weeks to days
- Years to days
- Milliseconds to days
- Microseconds to days
- Nanoseconds to days
- Decades to days
- Centuries to days
- Millennia to days
- Picoseconds to days
See all time units.