There are different calendars used worldwide but international standard is
gregorian calendar.
Second is the SI base unit of time and officially defined as the duration of 9
192 631 770 periods of the radiation corresponding to the transition between
the two hyperfine levels of the ground state of the caesium 133 atom.
This time conversion calculator converts the most common time units, second,
hour, minute, day, week, month, year, century and more.