The rai, Thai unit of area
The rai is exactly 1600 square meters, a square forty meters on a side. It is the unit in which Thailand writes its title deeds.
It divides into 4 ngan, and each ngan into 100 square wa of 4 square meters. That arithmetic holds because the Thai weights and measures act of 1923 fixed the wa at exactly two meters, tying the whole system to the meter without changing any of the numbers used on the ground. A chanote deed therefore still states an area as three numbers, rai, ngan and square wa, rather than in square meters.
The rai in other units
| 1 rai | 0.0016 km² |
| 1 rai | 0.16 ha |
| 1 rai | 16 a |
| 1 rai | 1,600 m² |
| 1 rai | 16,000,000 cm² |
| 1 rai | 0.000617763 mi² |
| 1 rai | 0.395369 ac |
| 1 rai | 17,222 ft² |
| 1 rai | 2,480,005 in² |
| 1 rai | 1,914 yd² |
| 1 rai | 1,600,000,000 mm² |
| 1 rai | 1.6 dunum |
| 1 rai | 484 tsubo |
| 1 rai | 0.380952 feddan |
| 1 rai | 484 pyeong |
| 1 rai | 9.14286 qirat |
| 1 rai | 15.8147 guntha |
| 1 rai | 39.5369 cent |
| 1 rai | 3.16295 kanal |
Frequently asked questions
How many rai make a hectare, and how many an acre?
6.25 rai to the hectare and 2.53 rai to the acre. The other way round, one rai is 0.395 acre, which is why a foreign developer happily rounds to two rai per acre and is twenty per cent out.
Why does Bangkok sell by the square wa and the provinces by the rai?
Because a city plot runs to tens of square wa: a townhouse sits on 20 to 50 square wa, that is 80 to 200 square meters. A paddy field is measured in rai, and the advertised price changes unit depending on which side of town you are buying.
What does a rai look like on the ground?
A square 40 meters on a side. A football pitch of 105 by 68 meters covers 4.46 of them, and a one-rai plot is roughly what a Thai developer cuts into ten townhouses.