There are five units in the long count: Bak'tun, K'atun, Tun, Winal, and K'in. They are as follows:

1 Bak'tun = 20 K'atun = 144,000 days

1 K'atun = 20 Tun = 7,200 days

1 Tun = 18 Winal = 360 days

1 Winal = 20 K'in = 20 days

1 K'in = 1 day

For reference, today would be labeled as 12 Bak'tun, 19 K'atun, 9 Tun, 12 Winal, 1 K'in in Long Count (using 584,285 correlation) by the Mayans. In modern notation, these numbers are given as a string of numbers, which looks like 12.19.9.12.1.

Sources:

"The Mayan Calendar", http://www.halfmoon.org/calfork.html

"Gregorian-Mayan Date", http://www.pauahtun.org/cgi-bin/gregmaya.py