Thailand adopted the metric system on 17 December 1923.[1]
Before metrication, the traditional system of measurement used in Thailand employed anthropic units. Some of these units are still in use, albeit standardised to SI/metric measurements. When the Royal Thai Survey Department began cadastral survey in 1896, Director R. W. Giblin, F.R.G.S., noted, "It so happens that 40 metres or 4,000 centimetres are equal to one sen," so all cadastral plans are plotted, drawn, and printed to a scale of 1:4,000.[2] The square wa, ngan and rai are still used in measurements of land area.
The baht is still used as a unit of measurement in gold trading. However, one baht of 96.5% gold bullion is defined as 15.16 grams rather than the generic standard of 15 grams. The baht has also become the name of the currency of Thailand, which was originally fixed to the corresponding mass of silver.
| Unit | Thai spelling | Pronunciation (IPA) | Meaning equivalent | Relative equivalent | Metric equivalent | |
|---|---|---|---|---|---|---|
| Length | ||||||
| Krabiat | กระเบียด | in Thai pronounced as /krā.bìat/ | Quarter of a finger | 0.5208 cm | ||
| Nio | นิ้ว | pronounced as /[níw]/ | Siamese inch[3] Cf. Digit (unit) finger (unit) | 4 krabiat | 2.083 cm | |
| Khuep | คืบ | pronounced as /[kʰɯ̂ːp]/ | Span | 12 nio | 25 cm | |
| Sok | ศอก | pronounced as /[sɔ̀ːk]/ | Cubit | 2 khuep | 50 cm | |
| Wa | วา | pronounced as /[wāː]/ | Fathom (outstretched arms) | 4 sok | 2 m | |
| Sen | เส้น | pronounced as /[sên]/ | Cf. Rope (unit) line of rope | 20 wa | 40 m | |
| Yot | โยชน์ | pronounced as /[jôːt]/ | Yojana | 400 sen | 16 km | |
| Area | ||||||
| Tarang wa | ตารางวา | pronounced as /[tāː.rāːŋ wāː]/ | Square wa | 4 m2 | ||
| Ngan | งาน | pronounced as /[ŋāːn]/ | 100 tarang wa | 400 m2 | ||
| Rai | ไร่ | pronounced as /[râj]/ | 4 ngan | 1,600 m2 (16 a) | ||
| Volume | ||||||
| Yip mue | หยิบมือ | pronounced as /[jìp mɯ̄ː]/ | Pinch | 7.8125 mL | ||
| Kam mue | กำมือ | pronounced as /[kām mɯ̄ː]/ | Grain held in an enclosed hand | 4 yip mue | 31.25 mL | |
| Fai mue | ฟายมือ | pronounced as /[fāːj mɯ̄ː]/ | Grain held in the palm | 4 kam mue | 125 mL | |
| Thanan | ทะนาน | pronounced as /[tʰā.nāːn]/ | Coconut shell used for measuring | 8 fai mue | 1 L | |
| Thang | ถัง | pronounced as /[tʰǎŋ]/ | Bucket | 20 thanan | 20 L | |
| Sat | สัด | pronounced as /[sàt]/ | Measuring basket | 25 thanan | 25 L | |
| Kwian | เกวียน | pronounced as /[kwīan]/ | Cartload | 100 thang | 2 m3 | |
| Weight/mass | ||||||
| Salueng | สลึง | pronounced as /[sā.lɯ̌ŋ]/ | 3.75 g | |||
| Baht or Bat | บาท | pronounced as /[bàːt]/ | 4 salueng | 15 g | ||
| Tamlueng | ตำลึง | pronounced as /[tām.lɯ̄ŋ]/ | Tael | 4 baht | 60 g | |
| Chang | ชั่ง | pronounced as /[t͡ɕʰâŋ]/ | Catty | 20 tamlueng | 1,200 g | |
| Hap | หาบ | pronounced as /[hàːp]/ | Picul | 50 chang | 60 kg | |