Pyeong-Tsubo Equivalence
Overview
Korea's pyeong and Japan's tsubo are the same quantity under two names: both denote the square of six shaku and both equal exactly 400/121 square metres, about 3.305785 m². The shared value is a consequence of shared history — the shakkanhō system was standardised in Meiji Japan with one shaku set at 10/33 metre, and that definition propagated across the region during the colonial period. A 30-pyeong Seoul apartment and a 30-tsubo Osaka house therefore enclose identical floor area, roughly 99.2 m². Usage has diverged even where arithmetic has not: Korean listings tend to quote supply area that includes shared circulation space, while Japanese practice more often reports exclusive floor area or land area. Both countries have removed the units from legally binding documents while leaving them dominant in conversation and marketing.
Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| $pyeong$ | Korean area unit | 평 | One square ken, 400/121 m². |
| $tsubo$ | Japanese area unit | 坪 | One square ken, numerically identical to the pyeong. |
Two Names, One Quantity
The Korean pyeong and the Japanese tsubo are the same unit:
$$1 \text{ pyeong} = 1 \text{ tsubo} = \frac{400}{121} \, m^2 \approx 3.305785 \, m^2$$
A 30-pyeong apartment in Seoul and a 30-tsubo house in Osaka enclose identical floor area, roughly 99.2 m². No conversion factor separates them; only the character used to write the unit differs — 평 in Korean, 坪 in Japanese, both descending from the same Chinese character.
Shared Origin
Both derive from the shakkanhō system standardised in Meiji Japan, where one shaku was fixed at 10/33 metre. Six shaku make one ken, and one square ken is the unit in question. Korea adopted the standardised definition during the colonial period, which is why the value is identical to the last digit rather than merely similar. Taiwan uses the same unit under the name ping (坪), with the same value.
Divergent Usage
Numerical identity has not produced identical practice.
| Korea (pyeong) | Japan (tsubo) | |
|---|---|---|
| Typical subject | Apartment supply area | Land area and floor area |
| Common quoted basis | Supply area including shared space | Exclusive floor area, land area |
| Legal status | Barred from commercial use, 2007 | Barred from official documents, 1951 |
| Everyday use | Dominant in conversation | Dominant in valuation and construction |
Korean supply-area convention means a 32-pyeong listing often describes a dwelling whose exclusive area is closer to 25 pyeong, a distinction that has no direct Japanese equivalent.
Derivation & History
The chain is short and exact: one shaku is 10/33 m by statute; one ken is six shaku, that is 20/11 m; one square ken is $(20/11)^2 = 400/121$ m². Because the Meiji definition was legislated rather than measured, every country that adopted it inherited an identical rational value. The alternative would have been independent national prototypes, which is what happened with the pre-1959 foot and produced the survey-foot discrepancy that United States land records carried for six decades.
Worked Examples
Comparing listings across two markets
- Both convert with the same factor: 30 × 3.305785 = 99.17 m²
- No cross-unit conversion is required
Result: Identical 99.2 m² in both markets
Taiwanese ping
- Taiwan uses the same 400/121 definition
- 22 × 3.305785 = 72.73 m²
Result: 72.7 m²
Edge Cases & Limitations
Supply versus exclusive area: The dominant practical difference between the two markets, and the reason equal unit counts can describe unequal homes.
Larger traditional units: Korea's danbo (300 pyeong) and Japan's tan (300 tsubo) also match, as do jeongbo and chō at 3,000. Rural land comparisons therefore also require no conversion.
Historical pre-Meiji values: Regional ken lengths varied before standardisation, so pre-modern documents cannot be converted with the modern factor.
Rounded published figures: Both markets round unit counts in advertising, so back-conversion to square metres reproduces the source only approximately.
Real-World Applications
Cross-border property investment between Korea, Japan and Taiwan, comparative housing-market research, construction cost benchmarking across the three markets, and translation of listings and appraisal reports all rely on the equivalence.