Thai land measurements explained: Rai, Ngan, and Square Wah

Thai land measurements explained simply: the system relies on three primary units—Rai, Ngan, and Square Wah—that do not align with the metric or imperial systems used in the West. For an investor or developer in Bangkok, miscalculating these units by even a small margin can lead to million-baht errors in valuation. The fundamental conversion to memorize is that one Rai equals 1,600 square meters. This unit is then subdivided into four Ngan, and each Ngan is further divided into 100 Square Wah. Therefore, one Square Wah (often called Talang Wah) is exactly four square meters. This is for real estate investors and developers who are evaluating land plots in Thailand and need to reconcile local listings with international construction standards. Understanding these ratios is the first step in determining the maximum buildable area under Bangkok zoning laws.

In the Thai property market, land is almost always quoted in this tripartite format: Rai-Ngan-Wah. For example, a listing might describe a plot as 2-3-50. This translates to 2 Rai, 3 Ngan, and 50 Square Wah. To find the total square meters, you would calculate (2 x 1,600) + (3 x 400) + (50 x 4), totaling 4,600 square meters. While condominiums are sold by the square meter (Talang Met), land is priced by the Square Wah. If a broker quotes a price of 500,000 THB per Square Wah in a prime area like Sukhumvit, you must be able to instantly convert that to 125,000 THB per square meter to compare it against construction costs or neighboring condo prices. This guide provides the technical framework to navigate these conversions without relying on third-party calculators that may round figures incorrectly.

Why It Matters Right Now

!Why It Matters Right Now visual for Thai land measurements explained: Rai, Ngan, and Square Wah Figure 1: Why It Matters Right Now

The timing for mastering Thai land measurements is critical due to the current property tax landscape and the updated land appraisal cycle. The Thai Treasury Department released its 2023-2026 land appraisal prices, which serve as the basis for property tax and transfer fee calculations. These appraisals are conducted on a per-Square Wah basis. In Bangkok's Central Business District, the gap between the Treasury Department's appraisal value and the market price can be significant: as of Q1 2024, Sukhumvit Soi 24-30 appraisal values sit at roughly 850,000 THB/Wah while market transactions exceed 2,200,000 THB/Wah—a 158% spread. Knowing the exact Square Wah count allows you to estimate your holding costs under the Land and Building Tax Act (effective 2020), which taxes land at 0.15% of appraised value for agricultural, 0.30% for residential, and 1.2% for commercial/industrial use. On a 500 Square Wah commercial plot appraised at 1,000,000 THB/Wah, annual tax is 6,000,000 THB (500 1,000,000 1.2%).

Furthermore, the Department of Lands has digitized roughly 85% of Bangkok land records into the LandsMaps application (iOS/Android), allowing instant verification of deed dimensions against GPS-surveyed boundaries. However, the physical title deed, or Chanote (Nor Sor 4 Jor), remains the ultimate legal authority. As Bangkok undergoes rapid densification along the MRT Orange Line (Western Section, target opening 2027) and Yellow Line (operational since July 2023), developers are competing for smaller, irregularly shaped plots. In these scenarios, a difference of 5 or 10 Square Wah (20-40 sqm) can be the deciding factor in whether a project meets the minimum 400 sqm land size requirement for a high-rise condominium under the Building Control Act B.E. 2522 (1979) as amended. Precise measurement is no longer just about price; it is about the legal feasibility of your investment.

The Play: Step-by-Step

!The Play: Step-by-Step visual for Thai land measurements explained: Rai, Ngan, and Square Wah Figure 2: The Play: Step-by-Step

To accurately value and verify land in Thailand, follow these steps to navigate the local measurement system.

1. Locate the measurement on the Chanote.

The front page of a Chanote (Title Deed) lists the land area in the top right or within the main body of the document. It will be written in the order of Rai, Ngan, and Square Wah. If a field is blank, it counts as zero. You must use the figures on the most recent original deed, as older photocopies may not reflect subsequent subdivisions or land surrenders for public roads. This step ensures you are working with the legally recognized area rather than a broker's estimate. Time estimate: 5 minutes.

1. Convert the tripartite units to Square Wah.

Since land pricing in Thailand is almost exclusively discussed in terms of "Price per Square Wah," you need a single number. Multiply the Rai by 400 and the Ngan by 100, then add the remaining Square Wah. For a 1-2-25 plot, the math is (1 x 400) + (2 x 100) + 25 = 625 Square Wah. This single unit is your primary tool for price negotiation and comparison. Time estimate: 2 minutes.

1. Calculate the total Square Meters for development.

Multiply your total Square Wah by four to get the square meterage. This is the figure you will provide to architects and contractors. In our 625 Square Wah example, the total is 2,500 square meters. This number is vital because the Bangkok City Plan (Zoning) defines the Floor Area Ratio (FAR) based on square meters. If the FAR is 6:1, you can build a total floor area of 15,000 square meters (2,500 x 6). Time estimate: 2 minutes.

1. Verify the boundary markers (Sao Khet).

Physically visit the site and locate the concrete boundary markers. Each marker has a unique serial number that corresponds to the land map held at the Department of Lands. If the physical distance between markers does not match the dimensions on the deed when converted to meters, you may have an encroachment issue. Use a laser measure (e.g., Bosch GLM 50-27 G, ~3,500 THB) to check the perimeter. One Wah is exactly 2 meters in length. Therefore, a plot that is 20 Wah wide should measure exactly 40 meters. Time estimate: 1-2 hours.

1. Cross-reference with Treasury Department Appraisals.

Visit the Treasury Department's appraisal portal and enter the title deed number and province. The system will provide the official value per Square Wah. Compare this to the asking price. If the asking price is 300,000 THB/Wah and the appraisal is 100,000 THB/Wah, your transfer fees (2% transfer fee + 0.5% stamp duty or 3.3% specific business tax if sold within 5 years + withholding tax 1% corporate/5-35% individual) will be based on the higher of appraised or sale price, but your annual land tax will be based on the 100,000 THB figure. Time estimate: 15 minutes.

1. Check for road setbacks and surrenders.

In Bangkok, the actual buildable area is often less than the measured land area. The Building Control Act requires setbacks from public roads based on the width of the road. Measure the road width in meters. If the road is less than 6 meters wide, your building must be set back at least 3 meters from the center of the road. This effectively reduces your usable square meterage, even if your Rai-Ngan-Wah count remains the same on paper. Time estimate: 30 minutes.

Real-World Example

Here is what this looks like in practice for a mid-sized developer evaluating a plot in the Phra Khanong district of Bangkok. The broker presents a land plot listed at 1-1-60 for a total price of 92,000,000 THB.

First, the investor converts the area into Square Wah to find the unit price.

• 1 Rai = 400 Square Wah
• 1 Ngan = 100 Square Wah
• Total = 400 + 100 + 60 = 560 Square Wah.

The price per Square Wah is 92,000,000 / 560 = 164,285 THB. The investor checks the Treasury Department 2023 appraisal for this specific sub-district and finds the official value is 120,000 THB per Square Wah. The market premium is roughly 37%.

Next, the investor converts the area to square meters to check development feasibility.

• 560 Square Wah x 4 = 2,240 square meters.

The plot is in an "Orange Zone" (Medium-Density Residential) with a Floor Area Ratio (FAR) of 5:1. This means the maximum Gross Floor Area (GFA) allowed is 2,240 x 5 = 11,200 square meters. However, the investor notices the access road is only 5 meters wide. Under the Bangkok Building Control Act, buildings taller than 8 meters on roads narrower than 6 meters face significant restrictions.

By understanding the measurements, the investor realizes that while they are paying for 2,240 square meters of land, the narrow road limits them to a low-rise luxury project rather than a high-density apartment block. The cost per buildable square meter (GFA) is 92,000,000 / 11,200 = 8,214 THB. This specific calculation, derived entirely from the Rai-Ngan-Wah conversion, allows the investor to determine if the project can achieve a 15% net profit margin after construction costs of approximately 25,000 THB per square meter.

Caveats

The Thai land measurement system is precise, but the documents recording them are not always updated. One common failure mode is relying on a "Nor Sor 3" or "Nor Sor 3 Gor" document rather than a Chanote (Nor Sor 4 Jor). Nor Sor 3 documents are not based on GPS surveys and can have area discrepancies of up to 10% when finally converted to a Chanote—as demonstrated in Supreme Court Case No. 4521/2565 where a 10-rai Nor Sor 3 plot in Samut Prakan was re-surveyed at 9 rai 2 ngan 50 wah (7.5% loss). Never commit capital to a land plot measured in Rai if the title deed is not a Nor Sor 4 Jor with a clear red Garuda emblem.

Another risk involves the "Price per Rai" trap in rural or peri-urban areas. Sellers may quote a price for a "Rai" that has not been officially surveyed in decades. In these cases, the physical boundaries (fences or trees) may have shifted. Always make the sale contingent on a new survey by the Department of Lands. A private licensed surveyor costs 15,000-30,000 THB for a standard sub-1-rai plot and takes 3-5 business days—minimal compared to the loss of 50 Square Wah (200 square meters) of land valued at 100,000 THB/Wah (20,000,000 THB).

Finally, remember that legal and tax content provided here is for general information. You must confirm all measurements and legal statuses with a licensed Thai lawyer or a qualified land surveyor before executing a purchase agreement. The 1,600 sqm conversion is a mathematical constant, but the legal right to build on those meters is subject to local municipal regulations that change frequently. Foreign buyers should note: direct land ownership is prohibited; structures include 30+30+30 year leaseholds, Thai company freehold (requiring 51% Thai shareholders), or BOI-promoted company exemptions.

Action Items

• Download the "LandsMaps" app (iOS: App Store, Android: Play Store) by the Thai Department of Lands. Enter the deed number and province to see digitized boundaries, official area in Rai-Ngan-Wah, and GPS coordinates of each Sao Khet marker. Overlay with Google Maps satellite view to spot encroachments before site visits.
• Create a spreadsheet with columns: Deed No., Rai, Ngan, Wah, Total Wah (=Rai400+Ngan100+Wah), Total Sqm (=Total Wah4), Asking Price/Wah, Treasury Appraisal/Wah, Premium %, FAR Zone, Max GFA, Road Width, Setback Loss (sqm), Net Buildable Sqm, Cost/Buildable Sqm. Formula for Total Sqm: `=(B21600)+(C2400)+(D24)`.
• Request a physical copy of the Chanote and verify: (1) Red Garuda emblem on every page, (2) Land Office stamp with date < 90 days old, (3) Page numbers sequential (e.g., 1/5, 2/5), (4) Owner name matches seller's ID, (5) No liens/encumbrances in "Rights and Burdens" section. Do not visit any site until this verification is complete.

If you are looking for more strategies on navigating the Thai property market and using AI to analyze local data, visit /newsletter.

Frequently Asked Questions

How many square meters are in one Rai of land?

There are exactly 1,600 square meters in one Rai. This is the standard conversion used by the Department of Lands for all official documentation and property tax assessments in Thailand. It is composed of four Ngan, with each Ngan equaling 400 square meters.

What is the difference between a Square Wah and a Square Meter?

One Square Wah (Talang Wah) is equal to four square meters (Talang Met). While square meters are used for internal building areas and condominiums, land in Thailand is legally measured and priced in Square Wah. A standard small townhouse plot in Bangkok is often around 20 to 50 Square Wah.

How do I convert Thai land measurements to acres?

One Rai is approximately 0.395 acres. To convert Rai to acres, multiply the number of Rai by 0.395. For a more precise calculation, since one acre is 4,046.86 square meters, one Rai (1,600 sqm) represents roughly 39.5% of an acre.

Why does the price of land use Square Wah instead of Rai?

Land is priced in Square Wah because it allows for more granular valuation, especially in high-value urban areas like Bangkok where a single Square Wah can cost over 1,000,000 THB. Using Rai for pricing would be too broad for small commercial or residential plots that are less than 1,600 square meters in size.