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The Wa (วา) is a traditional Thai unit of length. It is legally defined in relation to the metric system as exactly 2 meters.

The Wa serves as a fundamental unit within the traditional Thai system of measurement, particularly for land area. It is roughly equivalent to the distance between a person's outstretched fingertips when their arms are extended horizontally to the sides (similar to a fathom).

The Wa has been used in Thailand (formerly Siam) for centuries, likely originating from anthropomorphic measurements like the arm span. It was a practical unit for everyday measurements, construction, and land surveying.

• Traditional System: The Wa was part of a system that included smaller units like the khuep (span, ~25 cm), sok (cubit, ~50 cm, 1 Wa = 4 Sok), and larger units like the sen (rope, 1 Sen = 20 Wa).
• Standardization: During the modernization reforms under King Chulalongkorn (Rama V) in the late 19th and early 20th centuries, Thailand began standardizing its weights and measures. The Weights and Measures Act of 1923 formally defined traditional units in terms of the metric system. The Wa was officially set at exactly 2 meters.
• Metrication: While Thailand officially adopted the metric system as its primary standard, traditional units like the Wa remain legally defined and widely used, especially in specific contexts like land measurement.

The Wa's most significant modern use is in land measurement, but it historically had broader applications:

• Land Area: This is the most common contemporary use. Land area in Thailand is almost exclusively measured in Tarang Wa (ตารางวา - Square Wa).
  • 1 Tarang Wa = 4 square meters (2m x 2m)
  • 1 Ngan (งาน) = 100 Tarang Wa (400 sq m)
  • 1 Rai (ไร่) = 4 Ngan = 400 Tarang Wa (1600 sq m) Property deeds, real estate listings, and land surveys invariably use Rai, Ngan, and Tarang Wa.
• Length Measurement: While meters are now standard for most length measurements (textiles, construction materials), the Wa might still be used informally or in traditional contexts. Historically, it was used for measuring distances, building dimensions, rope lengths, etc.
• Construction & Architecture: Traditionally used for laying out building plots and determining dimensions in Thai architecture.
• Cultural Context: Understanding the Wa and its related area units is essential for navigating real estate, agriculture, and historical contexts in Thailand.