Calculate Average Month Length

Convert days and month. A calculator for the average length of months in a normal year and a leap year. A month doesn't have an exact length, but can have 28, 29, 30 or 31 days. 7 months have 31 days, 4 months have 30 days and February has 28 days in a normal year and 29 days in a leap year. So, if a number of months is given without an exact period of time, an average month length has to be estimated. This can be calculated here. Please select normal, average or leap year. An average year has 365.2421875 days. Then enter a number of months or days to calculate the other value.

Example: 200 days are a bit more than six and a half months. The difference between an average year, a normal year with 365 days or a leap year with one more day is only noticeable in the decimal places.

The name month refers to the moon. It takes between 29 and 30 days to orbit the earth. The year, i.e. the time it takes the earth to orbit the sun, cannot be divided without a remainder by the time it takes the moon to orbit the earth.
The ancient Romans divided the year into twelve months, and the names of the months come from Latin. The year originally began on March 1st, when the Roman consuls began their official duties. The last month was February, which only got the remaining days. Hence the names for the months September (septem = seven), October (octem = eight), November (novem = nine) and December (decem = ten) according to the original count. This was changed in 153 BC, since then the year begins on January 1st, and the names for these four months have been retained.