How is land measured in Thailand?

Land is measured in Rai, Ngan and Wah. 1 Rai = 4 Ngan (or 1600 Sqm.) 1 Ngan = 100 Wah (or 400 Sqm.) 1 Wah = 4 Sqm. 1 Acre = 2.5 Rai (approx.) 1 Hectare = 6.25 Rai (approx.)