Rai (unit)

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A rai (Thai: ไร่  [râj]) is a unit of area, equal to 1 square sen (เส้น) or 1,600 square metres (40 m × 40 m), and is used in measuring land area for a cadastre or cadastral map.[note 1] Its current size is precisely derived from the metre, but is neither part of nor recognized by the modern metric system, the International System (SI).

The rai equals 4 ngaan (Thai: งาน  [ŋāːn]) or 400 tarangwa (Thai: ตารางวา  [tāː.rāːŋ wāː]) aka square wa.

It is commonly used in Thailand and equals 16 ares, another unit that is based on the metre and commonly used in several countries. Although recognized by the SI, its use is not encouraged. The word also means plantation.

See also[edit]


  • "Units of Measurement". Thailand Guru, a service of Export Quality Services Co., Ltd. Retrieved 15 April 2007.  (which uses the name 'waa' instead of 'dtaaraangwaa' for the 'square waa')


  1. ^ Giblin, R. W. (2008) [1908]. "Chapter Royal Survey Work.". In Wright, Arnold; Breakspear, Oliver T. Twentieth century impressions of Siam (65.3 MB). London&c: Lloyds Greater Britain Publishing Company. at Work of the Deaprtment, p.126, para. 5. Retrieved January 28, 2012. "It so happens that 40 metres or 4,000 centimetres are equal to one sen, so all cadastral plans are plotted, drawn, and printed to a scale of 1:4,000." 

See also[edit]

  • 1 E+3 m² for a comparison with other areas
  • Area metric conversion, British and U.S., Japanese, Chinese, Thai, old French, old Spanish, old Russian, etc.