Measurements in Thailand

Reviewed by Wichuda Atthamethakon, LL.M., Thai Bar Licence 3149/2556, for ThaiLawOnline, a Thai law firm acting for foreigners since 2006.

Thailand adopted the metric system by the Weights and Measures Act of B.E. 2466 (1923). That Act is no longer the law. It was repealed, along with its 1933 and 1934 amendments, Revolutionary Council Announcement No. 171 of 1972 and the Act (No. 4) of B.E. 2526, by section 3 of the Weights and Measures Act B.E. 2542 (1999), which is the instrument in force today.

🔴 And the traditional Thai units are not folklore. They are lawful units of measurement. Section 9 of the 2542 Act provides that all weighing, measuring of capacity and measuring shall use the weights and measures of the metric system, or of the traditional system referred to the metric system as prescribed in the schedule annexed to this Act. So rai, ngan and square wah are not a rural survival that the law tolerates: they are defined in the Act’s own schedule, which is exactly why they appear on a Chanote and in the Land Department‘s own records. Section 10 lets the Minister, on the Committee’s advice, require the metric system alone for buying and selling in a given locality, so the position can be narrowed by announcement; but absent such an announcement a price quoted per square wah is quoted in a statutory unit.

Here are the conversions, with the statutory list separated from the customary units that guides usually print beside it:

Thai unit	Metric	Where the figure comes from
1 square wah (ตารางวา, ว๒)	4 square metres	Schedule, part B(2)
1 ngan (งาน, ง.) = 100 square wah	400 square metres	Schedule, part B(2)
1 rai (ไร่, ร.) = 4 ngan = 1 square sen	1,600 square metres	Schedule, part B(2)
1 khuep (คืบ, ค.)	one quarter of a metre, 25 cm	Schedule, part B(1)
1 sok (ศอก, ศ.) = 2 khuep	one half of a metre, 50 cm	Schedule, part B(1)
1 wa (วา, ว.) = 4 sok	2 metres	Schedule, part B(1)
1 sen (เส้น, ส.) = 20 wa	40 metres	Schedule, part B(1)
1 kwian luang (เกวียนหลวง, กว.)	2,000 litres	Schedule, part B(3)
1 ban luang (บั้นหลวง, บ.) = half a kwian	1,000 litres	Schedule, part B(3)
1 sat luang (สัดหลวง, ส.) = one fiftieth of a ban	20 litres	Schedule, part B(3)
1 thanan luang (ทะนานหลวง, ท.) = one twentieth of a sat	1 litre	Schedule, part B(3)
1 hap luang (หาบหลวง, ห.)	60 kilograms	Schedule, part B(4)
1 chang luang (ชั่งหลวง, ช.) = one hundredth of a hap	600 grams	Schedule, part B(4)
1 karat luang (กะรัตหลวง, กร.), gemstones only	1 metric carat, 20 centigrams	Schedule, part B(4)

Those fourteen are the whole of the statutory list, and the third column says so on purpose: they are copied from the schedule at the end of the Weights and Measures Act B.E. 2542 (1999), part B, traditional weights and measures referred to the metric system. Anything else you meet is custom or trade practice rather than a legal unit, and the common ones are worth naming because guides print them beside the statutory figures as though they were the same thing:

Customary unit	Usual value	Status
1 niu (นิ้ว), a finger-width	about 2.08 cm, being one twelfth of a khuep	Not in the schedule. 12 niu make the 25 cm khuep, so 2 cm flat does not add up
1 yot (โยชน์) = 400 sen	16 km	Not in the schedule; it follows from the sen
1 baht of gold ornament (ทองรูปพรรณ)	about 15.16 grams	Gold trade standard, not a statutory unit
1 baht of gold bar (ทองคำแท่ง)	about 15.244 grams	Gold trade standard, and it is not the same figure as the ornament baht
1 tamlung (ตำลึง) = 4 baht	about 60 grams	Customary, not in the schedule
1 chang, customary (ชั่ง) = 20 tamlung	about 1.2 kg	⚠️ Customary. The statutory chang luang is 600 grams, half this, which is why the schedule puts 100 chang in a hap and the customary ladder puts 50

1. Traditional Measurements in Thailand

These units are older than the metric system in Thailand, and they survived it because the law kept them rather than because the countryside did. You meet them most often on title deeds in Thailand and in property listings, where land is quoted in rai, ngan and square wah, and the figures below are the ones the Act fixes.

1. Wa (วา): one wa is 2 metres, and the schedule gives its abbreviation as ว. A plot is described by its frontage in wa and its area in square wah.
2. Ngan (งาน): One ngan is 400 square meters. Land measurements in Thailand often include ngan, especially when discussing property size.
3. Rai (ไร่, abbreviated ร.): one rai is 1,600 square metres, which is one square sen and about 0.395 of an acre. It is the standard unit for larger areas, and it is the unit a Chanote uses.

The law behind this page

English

Section 9 Weights and Measures Act B.E. 2542

Full text

All weighing, measuring of capacity and measuring of length shall use weights and measures in the metric system, or in the traditional system equated to the metric system as prescribed in the schedule to this Act.

ThaiLawOnline translation

Official text

Section 10 Weights and Measures Act B.E. 2542

Full text

Where, in the purchase, sale or distribution of any goods in any locality, the Minister, on the advice of the Committee, considers it appropriate to require the use of weights and measures solely in the metric system under section 9, or that it be carried out by any one of weighing, measuring capacity or measuring length, the Minister, on the advice of the Committee, has the power to prescribe this by notification. A notification under paragraph one takes effect on the expiry of 60 days from the date of its publication in the Royal Gazette.

ThaiLawOnline translation

Official text

Section 3 Weights and Measures Act B.E. 2542

Full text

The following are repealed: (1) the Weights and Measures Act, B.E. 2466; (2) the Weights and Measures Act (Amendment), B.E. 2476; (3) the Weights and Measures Act B.E. 2466 (Amendment), B.E. 2477; (4) Announcement of the Revolutionary Council No. 171 dated 30 June B.E. 2515; (5) the Weights and Measures Act (No. 4), B.E. 2526.

ThaiLawOnline translation

Official text

ไทย

มาตรา 9 พระราชบัญญัติมาตราชั่งตวงวัด พ.ศ. 2542

ข้อความเต็ม

การชั่ง การตวงและการวัดทั้งปวง ให้ใช้มาตราชั่งตวงวัดในระบบเมตริกหรือในระบบประเพณีที่เทียบเข้าหาระบบเมตริกตามที่กำหนดในบัญชีท้ายพระราชบัญญัตินี้

ตรงตามข้อความในราชกิจจานุเบกษา / สำนักงานคณะกรรมการกฤษฎีกา (Verbatim from the Royal Gazette / Office of the Council of State)

ข้อความทางการ

มาตรา 10 พระราชบัญญัติมาตราชั่งตวงวัด พ.ศ. 2542

ข้อความเต็ม

ในการซื้อขายหรือจำหน่ายสินค้าใด ๆ ในท้องที่ใด ถ้ารัฐมนตรีโดยคำแนะนำของคณะกรรมการเห็นสมควรให้ใช้มาตราชั่งตวงวัดเฉพาะในระบบเมตริกตามมาตรา ๙ หรือให้กระทำโดยการชั่ง การตวง หรือการวัดอย่างใดอย่างหนึ่ง ให้รัฐมนตรีโดยคำแนะนำของคณะกรรมการมีอำนาจประกาศกำหนด ประกาศตามวรรคหนึ่ง ให้ใช้บังคับเมื่อพ้นกำหนดหกสิบวันนับแต่วันประกาศในราชกิจจานุเบกษา

ตรงตามข้อความในราชกิจจานุเบกษา / สำนักงานคณะกรรมการกฤษฎีกา (Verbatim from the Royal Gazette / Office of the Council of State)

ข้อความทางการ

มาตรา 3 พระราชบัญญัติมาตราชั่งตวงวัด พ.ศ. 2542

ข้อความเต็ม

ให้ยกเลิก (๑) พระราชบัญญัติมาตราชั่งตวงวัด พระพุทธศักราช ๒๔๖๖ (๒) พระราชบัญญัติมาตราชั่งตวงวัด แก้ไขเพิ่มเติม พุทธศักราช ๒๔๗๖ (๓) พระราชบัญญัติมาตราชั่งตวงวัด พ.ศ. ๒๔๖๖ แก้ไขเพิ่มเติม พุทธศักราช ๒๔๗๗ (๔) ประกาศของคณะปฏิวัติ ฉบับที่ ๑๗๑ ลงวันที่ ๓๐ มิถุนายน พ.ศ. ๒๕๑๕ (๕) พระราชบัญญัติมาตราชั่งตวงวัด (ฉบับที่ ๔) พ.ศ. ๒๕๒๖

ตรงตามข้อความในราชกิจจานุเบกษา / สำนักงานคณะกรรมการกฤษฎีกา (Verbatim from the Royal Gazette / Office of the Council of State)

ข้อความทางการ

Français

Article 9 Weights and Measures Act B.E. 2542

Tout pesage, jaugeage et mesurage se fait selon le système métrique ou le système traditionnel converti en système métrique, comme prévu à l'annexe de la loi.

résumé non officiel

Texte officiel

Article 10 Weights and Measures Act B.E. 2542

Sur avis du comité, le ministre peut imposer par avis, pour la vente de marchandises dans une localité, le seul système métrique de l'article 9 ou un mode déterminé de pesage, de jaugeage ou de mesurage, applicable à l'expiration de 60 jours après publication au Journal officiel.

résumé non officiel

Texte officiel

Article 3 Weights and Measures Act B.E. 2542

Sont abrogés la loi sur les poids et mesures de B.E. 2466, ses lois modificatives de B.E. 2476, B.E. 2477 et B.E. 2526 (n° 4), ainsi que l'annonce n° 171 du Conseil révolutionnaire du 30 juin B.E. 2515.

résumé non officiel

Texte officiel

Sources

• Weights and Measures Act B.E. 2542, retrieved 2 November 2026

2. Metric System

Thailand now uses the metric system for measurements, following global standards to stay consistent and compatible with international norms. It is used for:

• Length: Meters and kilometers are standard for distance.
• Weight: Grams and kilograms are used for weight. If you’re at a market, you’ll often buy fruits and vegetables by the kilogram.
• Volume: Liters and milliliters are the norm for liquids. Gas stations sell fuel by the liter, and you’ll buy bottled water in liters.

3. Everyday Measurements in Thailand

Throughout your daily routines, it’s common to come across a blend of various systems, each contributing its unique characteristics and functionalities to the overall landscape of your experiences.

• In Thailand, land and property are measured using traditional units such as rai, ngan, and wa, as well as square meters. Rai, ngan, and wa are commonly used units of measurement for real estate in Thailand. Additionally, square meters are also used to measure land and property in the country.
• Shopping: Grocery stores and markets use kilograms for produce and grams for smaller items like spices.
• Construction: Builders often use meters and centimeters for measurements but might refer to traditional units for land size.

4. Practical Tips about Measurements in Thailand

1. Conversion: Familiarize yourself with basic conversions. For example, 1 wa equals 2 meters, 1 rai equals 1,600 square meters, and so on.
2. Ask for Clarity: When in doubt, ask for measurements in the system you’re most comfortable with. Most locals are familiar with both and can help translate.
3. Legal Documents: Ensure all legal documents, especially those related to property, clearly state measurements in both traditional and metric units to avoid any misunderstandings.

FAQS about Measurements in Thailand

Understanding the mix of traditional and metric systems in Thailand is key to navigating daily life and legal matters efficiently. Start by familiarizing yourself with the basic conversions, ask for clarity when needed, and ensure legal documents are precise. This knowledge will help you feel more confident and connected in your interactions and transactions in Thailand.

Last reviewed: 5 September 2026. Every conversion on this page was read against the instrument that fixes it: the schedule annexed to the Weights and Measures Act B.E. 2542 (1999), part B, traditional weights and measures referred to the metric system, taken from the consolidated Thai text, together with section 3 of that Act, which repealed the Weights and Measures Act of B.E. 2466 and its amendments, section 9, which makes both the metric system and the scheduled traditional units lawful for all weighing and measuring, and section 10, under which the Minister may require the metric system alone in a given locality for buying and selling. Four things were corrected as a result: the page named the repealed 1923 Act as the law and did not mention the Act in force; it presented the traditional units as a rural custom when the statute defines them; its conversion table contradicted itself three times over, on the baht against the tamlung, on the niu against the khuep, and on the chang against the hap; and it gave the chang as 1.2 kg where the schedule fixes the chang luang at 600 grams. The area conversions, the rai to acre and hectare arithmetic and the worked examples in the questions below were all checked and were already right.

What this review does not cover. The units in the second table are labelled as customary or trade figures precisely because no instrument we can produce fixes them: the niu, the yot, the tamlung, the customary chang and both gold baht are market and everyday usage, and the two gold figures in particular are set by the gold trade rather than by law, so confirm them with the shop. Nothing on this page about utility billing, internet speeds, air-conditioner BTU ratings, fuel grades or recipe spoon sizes was verified against a source; those are everyday practice and are presented as such.

• Systems of Units Measurements Wikipedia

Land in Thailand is titled and sold in rai, ngan and square wah, which is where these units matter most. Our property guide for foreigners covers what a foreigner can actually hold.