Month (mo) - Unit Information & Conversion
What is a Month?
Definition
A month is a unit of time, used with calendars, that is approximately based on the orbital period of the Moon around the Earth. In the Gregorian calendar, a month can have 28, 29, 30, or 31 days. For conversions, an average month is often defined as 1/12th of a year, which is approximately 30.44 days (365.25 days / 12 months).
History
The concept of the month originated from observing the lunar cycle (the period from one new moon to the next, about 29.5 days). Early calendars, like the Roman calendar, were often lunar or lunisolar. The Gregorian calendar, now used internationally, standardized the month lengths (mostly 30 or 31 days) to align the calendar year more closely with the solar year, largely detaching the calendar month from the strict lunar cycle.
Common Uses
- Calendars: The primary division of the year for dating and scheduling longer-term events.
- Billing & Finance: Common cycle for salaries, rent/mortgage payments, subscriptions, bank statements, and financial reporting.
- Planning: Used for medium-term planning (monthly goals, project milestones).
- Time Measurement: Expressing durations longer than weeks (e.g., project duration, age of infants, gestation periods).
- Seasonality: Often associated with seasonal changes, although this varies by month and hemisphere.
Unit FAQs
How many days are in a month?
It varies: 30 days (April, June, September, November), 31 days (January, March, May, July, August, October, December), or 28/29 days (February).
Why do months have different lengths?
The varying lengths are a historical artifact from the Roman calendar adjustments, refined in the Julian and Gregorian calendars, aimed at aligning the calendar year with the solar year while maintaining 12 months.
What is an average month length used for conversions?
For calculations, an average month is often taken as 30.4375 days (365.25 days / 12 months).
Is a month based on the Moon?
Historically, yes. The word "month" is related to "Moon". However, in the Gregorian calendar, the link is approximate; calendar months don't precisely track the lunar phases.
Month Conversion Formulas
To Second:
To Minute:
To Hour:
To Day:
To Week:
To Year:
To Millisecond:
To Microsecond:
To Nanosecond:
To Decade:
To Century:
To Millennium:
To Fortnight:
To Planck Time:
To Shake:
To Sidereal Day:
To Sidereal Year:
Convert Month
Need to convert Month to other time units? Use our conversion tool.