The ''rai'',, . ''ngan'', and ''tarang wa'' or ''square'' wa are customary

Thai units Thailand adopted the metric system on 17 December 1923.area Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape A shape or figure is a graphics, graphical representation of an obje ...

, used in the measurement of land. They are defined as exactly 1,600, 400, and 4

square metre The square metre ( international spelling as used by the International Bureau of Weights and Measures) or square meter (American spelling) is the unit of area in the International System of Units (SI) with symbol m2. It is the area of a square w ...

s, respectively (17,222, 4,306, and 43 sq ft). The ''tarang wa'' (square ''wa'', ''tarang'' meaning 'grid') is derived from the area of a square with sides of 1 '' wa'' (the Thai

fathom A fathom is a unit of length in the imperial and the U.S. customary systems equal to , used especially for measuring the depth of water. The fathom is neither an International Standard (SI) unit, nor an internationally-accepted non-SI unit. Hi ...

). One ''ngan'' is equal to 100 square ''wa'', and one ''rai'' ('field' or 'plantation') equals 4 ''ngan'' or 1 square '' sen''. The units were standardized in square metres when Thailand (then Siam) adopted the

metric system The metric system is a system of measurement that succeeded the Decimal, decimalised system based on the metre that had been introduced in French Revolution, France in the 1790s. The historical development of these systems culminated in the d ...

in 1923, although the Royal Survey Department was already reported in 1908 to be using the metre-based conversion for its

cadastral maps A cadastre or cadaster is a comprehensive recording of the real estate or real property's metes-and-bounds of a country.Jo Henssen, ''Basic Principles of the Main Cadastral Systems in the World,'/ref> Often it is represented graphically in a ca ...

. 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.

Notes

References

{{reflist Thai units of measurement Units of area