Rai, ngan, and tarang wa

The rai, ngan, and tarang wa or square wa are customary Thai units of area, used in the measurement of land. They are defined as exactly 1,600, 400, and 4 square metres, respectively.
The tarang wa is derived from the area of a square with sides of 1 wa. 1 ngan is equal to 100 square wa, and 1 rai equals 4 ngan or 1 square sen. The units were standardised in square metres when Thailand adopted the metric system in 1923, although the Royal Survey Department was already reported in 1908 to be using the metre-based conversion for its cadastral maps.
The units are commonly used for cadastre and property matters, and official and legal documents express areas of land in such units. They are sometimes notated in the abbreviated format rai-''ngan-tarang wa, e.g. "4-2-25 rai", which means "4 rai, 2 ngan, and 25 tarang wa", though this is discouraged by some government documents.
Unit Derivation Relative SI US or UK customary
Tarang wa Square wa 4 m² 43 sq ft
Ngan 100 tarang wa 400 m² 4,306 sq ft
Rai Square sen 4 ngan or 400 tarang wa'' 1,600 m² 17,222 sq ft

Unit	Derivation	Relative	SI	US or UK customary
Tarang wa	Square wa		4 m²	43 sq ft
Ngan		100 tarang wa	400 m²	4,306 sq ft
Rai	Square sen	4 ngan or 400 tarang wa''	1,600 m²	17,222 sq ft