Traditional Length Converter (치·자·간·리 / 寸·尺·間·里)

Understanding the traditional length converter (ja, gan, ri) — concept and principle

Before the metric system, Korea and Japan measured length in chi/sun (치·寸), ja/shaku (자·尺), gan/ken (간·間), jeong/chō (정·町) and ri (리·里). These units still appear in hanok carpentry, old building plans and land documents, classical literature, proverbs such as "ten ri" and sayings about a person's height in ja. This converter changes any of these units into another or into metres and centimetres.

How it is calculated

Every unit is first converted into ja (shaku), then into the target unit:

• 1 ja = 10/33 m ≈ 30.303 cm, so 1 m = 3.3 ja
• 1 chi = 0.1 ja ≈ 3.03 cm
• 1 gan = 6 ja ≈ 1.818 m
• 1 jeong = 60 gan = 360 ja ≈ 109.1 m
• Korean 1 ri = 1,296 ja ≈ 392.7 m (one tenth of the Japanese ri)
• Japanese 1 ri = 36 jeong = 12,960 ja ≈ 3.927 km

Result = value × (size of source unit in ja) ÷ (size of target unit in ja).

The principle

The traditional units are a chain of fixed multiples, so only one of them needs a link to the metre. Japan's Weights and Measures Act of 1891 fixed the shaku at exactly 10/33 m, and the same ja was used in Korea during the first half of the 20th century. That single definition makes every other conversion exact. Korea's Measures Act of 1961 later made the metric system the legal standard. Note that a Korean speaker's "ri" (as in 십 리) is about 0.4 km, while the Japanese ri is about 3.9 km; mixing them up gives an error of ten times.

Worked example

1. Default inputs: value 1, from gan, to metres.
2. 1 gan = 6 ja.
3. 6 × 10/33 m = 60/33 m = 1.818181818 m.
4. The same value in other units: 6 ja, 60 chi, about 181.8 cm, 1/60 jeong ≈ 0.0166666667.

How to read the result

For daily use, 1 ja is about 30 cm, 1 gan about 1.8 m and 10 Korean ri about 4 km. In hanok, "칸" or "간" also names one bay between columns, and the actual spacing of a bay varies from building to building, so check the drawing or measure on site rather than assuming 6 ja. Older Korean ja standards before the 20th century also differed by use (for example rulers for building, cloth or rituals), so pre-modern texts may not match 30.3 cm.

Common mistakes

• Using the Japanese ri for a Korean phrase such as "10 ri", which turns 4 km into 39 km.
• Assuming every hanok bay is exactly one 6-ja gan.
• Confusing the length gan with the area pyeong (1 pyeong is 1 gan × 1 gan).

Frequently asked questions

How long is 1 ja (자)?

10/33 m, about 30.3 cm.

How many km is 10 ri (십 리)?

With the Korean ri of about 392.7 m, 10 ri is about 3.93 km, usually said as "about 4 km".

How is gan related to pyeong?

One pyeong is a square 1 gan on each side: (60/33 m)² = 400/121 m² ≈ 3.306 m².

How many ja is a person 170 cm tall?

1.70 × 3.3 = 5.61 ja, or about 5 ja 6 chi.

Sources: Japan, Weights and Measures Act (度量衡法), 1891 · Republic of Korea, Measures Act (계량법), 1961