Thai land measurements are a combination of imperial and metric measurement systems. Title deeds in Thailand include all land measurements using the Thai system and are also written in Thai, therefore it is beneficial for you to have a translation if you are thinking of buying a property. Below you'll find a comparison between the Thai and Western sytems which hopefully will help you gain a better understanding.
1 Wah = 2 Metres
1 Sq Wah is called a Talangwah = 4 Sqm
100 Talangwah = 1 Ngan = 400 Sqm
4 Ngan = 1 Rai = 1600 Sqm = 400 Talangwah
1 Acre = 4047 Sqm = approx 2.53 Rai
1 Hectare = 10000 Sqm = 6.25 Rai