Tsubo to Square Meters
Overview
Japanese property is still discussed in tsubo, a unit equal to the square of six shaku and therefore identical to 400/121 square metres, approximately 3.3058 m². A 25-tsubo house occupies about 82.6 m². The unit descends from the shakkanhō system codified in the Meiji period, when one shaku was fixed at 10/33 metre to bridge the traditional measure and the metric system Japan had just joined. The Measurement Act of 1951 restricted tsubo from official transactions, and contracts must state square metres, but land prices are routinely quoted per tsubo and construction estimates are budgeted the same way. Because the tsubo and the Korean pyeong share one definition, floor areas convert between the two markets without any numerical change — only the name differs.
Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| $tsubo$ | Area in tsubo | 坪 | Traditional Japanese unit of area, one square ken. |
| $m²$ | Area in square metres | m² | Metric equivalent required on Japanese contracts. |
The Unit Japanese Property Still Speaks
Japanese land and buildings are discussed in tsubo, the square of one ken, equal to exactly 400/121 square metres:
$$m^2 = tsubo \times 3.3058$$
A 25-tsubo house occupies about 82.6 m², and a 40-tsubo plot about 132.2 m².
Where the Unit Persists
The Measurement Act of 1951 restricted tsubo from official transaction documents, which must state square metres. In practice the unit survives everywhere the metric figure is not legally required:
- Land prices are quoted per tsubo (tsubo tanka), the headline number in valuation
- Construction costs are budgeted per tsubo of floor area (tsubo tanka again, in a different sense)
- Real-estate advertising states both, with tsubo given prominence
- Interior fit-out and renovation quotes price by tsubo
Reading a Japanese Listing
A property advertisement typically reports land area, building area and total floor area separately, each in square metres with a parenthetical tsubo figure. Because one tsubo is roughly two tatami mats, a floor area in tsubo also gives a quick sense of room count in traditional construction.
Relation to the Korean Pyeong
The tsubo and the Korean pyeong share one definition and one numerical value, a direct consequence of the shakkanhō system spreading across the region. Floor areas therefore transfer between the two property markets without any arithmetic beyond a change of name.
Derivation & History
One shaku was fixed by Meiji legislation at 10/33 metre. One ken is six shaku, or 20/11 metre — approximately 1.8182 m — and one tsubo is one square ken, giving $(20/11)^2 = 400/121 = 3.30578512\ldots$ m². The ken was not an arbitrary length: it is the standard column spacing of traditional timber framing, so a building's footprint in tsubo counts structural bays directly. That is why traditional plans resolve to whole tsubo without remainder and why the unit remains natural to Japanese builders.
Worked Examples
Land price per tsubo
- Convert area: 165.29 ÷ 3.3058 = 50.0 tsubo
- Divide the price: 42,000,000 ÷ 50 = 840,000
Result: 840,000 yen per tsubo
Construction budget
- Metric floor area: 30 × 3.3058 = 99.2 m²
- Budget: 30 × 900,000 = 27,000,000 yen
Result: 99.2 m², about 27 million yen
Edge Cases & Limitations
Land versus floor area: A listing's tsubo figure may describe the plot, the building footprint or total floor area across storeys. Each is a different quantity.
Tan and cho: Agricultural land uses tan (300 tsubo) and cho (3,000 tsubo); confusing them with tsubo misstates area by three orders of magnitude.
Rounded advertising figures: Tsubo values in listings are usually rounded to one decimal, so back-conversion will not exactly reproduce the registered square metres.
Setback and coverage rules: Buildable area is constrained by coverage and floor-area ratios, so plot tsubo does not translate directly into permitted construction.
Real-World Applications
Land valuation, construction cost estimation, commercial rent quotation, property tax discussion and interior renovation pricing all operate in tsubo. The National Tax Agency's published land valuations and the annual official land price survey are reported per square metre, requiring conversion when compared with market quotes.