The ancient Chinese units of length is based on CHI(尺), and most other units are decimal multiples or fractions of it.

Decimal UnitsEdit

Unit name Definition Multiples of CHI Similar Western units
WEI 1/10 of HU 10-7 None
HU 1/10 of MIAO 10-6 None
MIAO 1/10 of HAO 10-5 None
HAO 1/10 of LÍ 10-4 None
1/10 of FEN 0.001 Point
FEN 1/10 of CUN 0.01 Line
CUN 1/10 of CHI 0.1 Inch
CHI Base Unit 1 Feet
ZHANG 10 CHI 10 None
YIN 10 ZHANG 100 None

The FEN was originally the width of a millet corn.

The CUN came from the width of a finger, and the CHI was a man's span. Later, they were defined as 1 CHI = 10 CUN = 100 FEN.

Non–Decimal UnitsEdit

Unit name Definition Multiples of CHI Similar Western units
ZHI 8 CUN 0.8 Span
XUN 8 CHI 8 None
CHANG 2 XUN 16 Perch
REN ≈the distance between a man's outstretched arms (See below) Fathom
BU ≈Two steps 5 or 6 Pace
300 BU 1500 or 1800 None

ZHI was a woman's span, and then defined as 0.8 CHI. So There's a word Zhichi means 'Very near'.

XUN and REN had the same origin, but XUN was defined as 8 CHI and REN wasn't.

REN was only used for measuring depth. Because the CHI is changed, the ratio of REN and CHI changed from 8 to 7 and then 5.6 . Someone also thought REN was half of XUN (as yard) so 4 CHI.

LǏ is a common units for measuring long distances.

Different lengthsEdit

before Sui dynastyEdit

Shang Dynasty(17th century BCE — 11th century BCE):1 CHI = 17 cm (based on ancient bone rulers)

Zhou, Qin & Western Han Dynasty(11th century BCE — 24 CE): 1 CHI = 23.1 cm (based on ancient bronze rulers)

astern Han & Three-Nation Dynasty(25 CE — 265 CE): 1 CHI = 24 cm (based on ancient wooden rulers)

Jin & South Dynasty(265 CE — 589 CE): 1 CHI = 24.5 cm (based on records on the book)

North Dynasty(386 CE — 581 CE): 1 CHI = 27~30 cm (changing in almost every decade)

Astronomical–Musical CHI since Sui DynastyEdit

The Astronomical-Musical CHI between Sui and Early Qing Dynasty(581 CE — about 18th century) is always 24.5 cm long. The changing is so small that is not important.

At Kangxi times, The Astronomical CHI was set to the Mechanical CHI, and the Musical CHI = 0.81 Mec.CHI =25.92 cm.

Normal CHI since Sui DynastyEdit

Sui & Tang & Five-short Dynasty(581 CE — 960 CE): 1 CHI = 30 cm (based on ancient rulers)

Song & Yuan Dynasty(960 CE — 1368 CE): 1 CHI = 31.6 cm

In Ming and Qing Dynasty, the Normal CHI became 3 different lengths: Mechanical, Cloth, Survey.

Ming Dynasty(1368 CE — 1644 CE): 1 Mec. CHI = 32 cm, 1 Clo. CHI = 34 cm, 1 Sur. CHI = 0.96 Clo. CHI = 32.6 cm.

Qing Dynasty & Early ROC(1644 CE — 1915 CE): 1 Mec. CHI = 32 cm, 1 Clo. CHI = 10/9 = 35.6 cm, 1 Sur. CHI = 0.96 Clo. CHI = 34.5 cm.

In 1915, the ROC Peking government abolished Cloth CHI and Survey CHI.

Metre-based definitionEdit

In Qing dynasty, people found that 1 m = 3.125 CHI, and that becomes a de facto standard.

In 1915, the ROC Peking government made this conversion legal. ('The CHI is Thirty-Two per cent of the Length between Two Marks on the Platinum-Iridium Bar at Zero Degrees centigrade.')

in 1929, the ROC Nanking government redefined the old units as the French Mesures usuelles. The New CHI is a third of the metre.

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