Converting Rai and Wah can be complex and can create legal issues when people do not understand what it is that they are signing at the contract stage. These are the basics for land conversion in the land measurement system in Thailand. Thailand does not have an Imperial or Metric system.
1 sq. wah = 4 sq. m. 1 acre = 2.471 rai or 43,560 sq. ft.
1 ngan = 100 wah (or 400 sq. m.) 1 hectare = 6.25 rai or 10,000 sq. m.