Traditional units of measurement in Japan
East Asia · 11 documented units · reviewed 2026-07-31
Quick answer
Japan’s shakkanho system survives in real estate and carpentry: 1 tsubo = 3.3058 m², 1 shaku = 10/33 m, 1 momme = 3.75 g.
How measurement works in Japan
The shakkanho was formally replaced by SI for trade in 1966, but property listings still quote floor area in tsubo and room size in jo (tatami mats), and traditional carpentry still works in shaku, sun and ken.
Because the shaku was tied to the metre as exactly 10/33 m, the whole system is exactly convertible — tsubo, jo and ken all derive from that definition rather than from a physical standard.
Momme survives internationally in the pearl trade, where pearl weight is still quoted in momme worldwide, and koku survives in historical and sake-industry contexts.
area units of Japan
| Unit | Value in SI | Typical use | Convert |
|---|---|---|---|
| Tsubo (坪) | 1 Tsubo (坪) = 3.306 square metre | surveying | Tsubo (坪) → square metresIn-depth guide |
| Jō (畳/Tatami) | 1 Jō (畳/Tatami) = 1.653 square metre | surveying | Jō (畳/Tatami) → square metresIn-depth guide |
mass units of Japan
| Unit | Value in SI | Typical use | Convert |
|---|---|---|---|
| Momme | 1 Momme = 0.00375 kilogram | jewellery, precious-metals, textiles | Momme → kilogramsIn-depth guide |
| Kan | 1 Kan = 3.75 kilogram | trade | Kan → kilograms |
length units of Japan
| Unit | Value in SI | Typical use | Convert |
|---|---|---|---|
| Shaku (Japanese) | 1 Shaku (Japanese) = 0.303 metre | textiles, general | Shaku (Japanese) → metresIn-depth guide |
| Sun (Japanese) | 1 Sun (Japanese) = 0.0303 metre | general | Sun (Japanese) → metres |
| Ken (Japanese) | 1 Ken (Japanese) = 1.818 metre | surveying | Ken (Japanese) → metresIn-depth guide |
| Ri (Japanese Mile) | 1 Ri (Japanese Mile) = 3,927 metre | navigation | Ri (Japanese Mile) → metresIn-depth guide |
volume units of Japan
| Unit | Value in SI | Typical use | Convert |
|---|---|---|---|
| Koku (石) | 1 Koku (石) = 180.39 litre | agriculture, trade | Koku (石) → litresIn-depth guide |
| Gō (合) | 1 Gō (合) = 0.1804 litre | cooking | Gō (合) → litresIn-depth guide |
| Shō (升) | 1 Shō (升) = 1.804 litre | cooking, trade | Shō (升) → litres |
Before you convert
- A jo is not a fixed area nationwide: Kyoto-ma, Chukyo-ma and Edo-ma tatami differ, so listings state which standard applies.
- Tsubo figures in listings are usually rounded to two decimals; do not treat a reverse conversion as exact.
Sources
- Japanese Measurement Act (計量法), 1951 and 1966 amendments
See our methodology and data provenance pages, or review published corrections.