Dzongkha, the national language of Bhutan, has two numeral systems, one vigesimal (base 20), and a modern decimal system. The vigesimal system remains in robust use. Ten is an auxiliary base: the -teens are formed with ten and the numerals 1–9. Ex. cu_ci

## Vigesimal

Hindu-Arabic numerals Dzongkha numerals Spelling Romanisation
1 ཆཱི chiː
2 ཉྱཱི ˈɲyiː
3 སུམ sum
4 ཞི ʑhi
5 ˈŋga
6 ཌཱུ ɖʱuː
7 དྱཱུན dyûn
8 གཻ ɡeː
9 གཱུ ɡuː
10 ༡༠ ཅུཐཱམ cu-tʰãm*
11 ༡༡ ཅུཅི cu-ci
12 ༡༢ ཅུཉི cu-ɲi
13 ༡༣ ཅུསུམ cu-sum
14 ༡༤ ཅུཞི cu-ʑi
15 ༡༥ ཅེངཱ ce-ŋa
16 ༡༦ ཅུཌུ cu-ɖu
17 ༡༧ ཅུཔྡྱ cup-dỹ
18 ༡༨ ཅོཔྒེ cop-ɡe
19 ༡༩ ཅྱགུ cy-ɡu
20 ༢༠ ཁེཆཱི kʰe ciː

*When it appears on its own, 'ten' is usually said cu-tʰãm 'a full ten'. In combinations it is simply cu.

Multiples of 20 are formed from kʰe. Intermediate multiples of ten are formed with pɟʱe-da 'half to':

 30 kʰe pɟʱe-da ˈɲiː (a half to two score) 40 kʰe ˈɲiː (two score) 50 kʰe pɟʱe-da sum (a half to three score) 100 kʰe ˈŋa (five score) 200 kʰe cutʰãm (ten score) 300 kʰe ceŋa (fifteen score)

400 (20²) ɲiɕu is the next unit: ɲiɕu ciː 400, ɲiɕu ɲi 800, etc. Higher powers are 8000 (20³) kʰecʰe ('a ɡreat score') and jãːcʰe 160,000 (20⁴).

## Decimal

The decimal system is the same up to 19. Then decades, however, are formed as unit–ten, as in Chinese, and the hundreds similarly. 20 is reported to be ɲiɕu, the same as vigesimal numeral 400; this may be lexical interference for the expected *ɲi-cu. (In any case, there is no ambiguity, because as 400 it is obligatorily ɲiɕu ciː 'one 400'.) Several of the decades have an epenthetic -p-, perhaps by analogy with 18 and 19, where the -p- presumably reflects a historical *cup 'ten':

sum-cu 30, ʑi-p-cu 40, ˈŋa-p-cu 50, ɟa-tʰampa or cik-ɟa 100 (a 'full hundred' or 'one hundred'), ɲi-ɟa 200, sum-ɟa 300, ʑi-p-ɟa 400, etc.