How many days are there in a month?

There are 28 days, 29 days, 30 days and 3 1 day in a month. The number of days in a month in the lunar calendar is 29 or 30 days according to the orbit of the moon around the earth. The big month in the solar calendar is 3 1 day, the small month is 30 days, the February in the solar calendar is called the flat month or the flat month is 28 days, and the flat month in the leap year in the solar calendar is 29 days, that is, February 29 is a leap day.