Since Calendar Round dates can only distinguish in 18,980 days, equivalent to around 52 solar years, the cycle repeats roughly once each lifetime, and thus, a more refined method of dating was needed if history was to be recorded accurately. To measure dates, therefore, over periods longer than 52 years, Mesoamericans devised the Long Count calendar.
The Maya name for a day was
k'in. Twenty of these k'ins are known as a
winal or
uinal. Eighteen winals make one
tun. Twenty tuns are known as a
k'atun. Twenty k'atuns make a
b'ak'tun.
The Long Count calendar identifies a date by counting the number of days from August 11, 3114 BCE in the
proleptic Gregorian calendar or September 6 in the
Julian calendar. But instead of using a base10 (
decimal) scheme like Western numbering, the Long Count days were tallied in a modified base20 scheme. Thus 0.0.0.1.5 is equal to 25, and 0.0.0.2.0 is equal to 40. As the winal unit resets after only counting to 18, the Long Count consistently uses base20 only if the tun is considered the primary unit of measurement, not the k'in; with the k'in and winal units being the number of days in the tun. The Long Count 0.0.1.0.0 represents 360 days, rather than the 400 in a purely base20 (
vigesimal) count.
Table of Long Count units Days  Long Count period  Long Count period  Approx solar years 
1  = 1 K'in 


20  = 20 K'in  = 1 Winal  1/18th 
360  = 18 Winal  = 1 Tun  1 
7,200  = 20 Tun  = 1 K'atun  20 
144,000  = 20 K'atun  = 1 B'ak'tun  395 
There are also four rarelyused higherorder cycles:
piktun,
kalabtun,
k'inchiltun, and
alautun.
Since the Long Count dates are unambiguous, the Long Count was particularly well suited to use on monuments. The monumental inscriptions would not only include the 5 digits of the Long Count, but would also include the two tzolk'in characters followed by the two haab' characters.