What base system did the Maya use for counting?

What base system did the Maya use for counting? The answer is vigesimal, or base 20.

Maya numerals used a positional vigesimal system: each place generally represented a power of 20. The system was built from a small set of symbols—a dot for one, a bar for five, and a shell-like sign for zero. Combining these symbols allowed the Maya to record both everyday quantities and enormous chronological totals.

For example, a digit in the second position represented twenties, while the third represented 400s. A numeral consisting of one twenty-place unit and thirteen units therefore represented 33. Numbers were commonly arranged vertically, with higher place values above lower ones.

The calendar introduced an important modification. In the Long Count, the place after 20 days was a tun of 360 days rather than 400, probably because it approximated the length of a solar year. This does not change the general answer: Maya counting was vigesimal. A common mistake is to call it decimal simply because modern explanations write Maya values using Arabic numerals.