Si (length)

Si is a traditional Chinese unit of length. One si is equal to 1/10 of a hao, 1/100 000 of a chi, or 3+1⁄3 μm. In the field of engineering, one si equals 10 μm.

Present law on Chinese length units

This law of length measurement was issued by the Chinese government in 1929, and has been effective since 1 January 1930. The base unit chi is defined to be 1/3 meter.

These units are based on the metric system. The Chinese word for metre is 米 mǐ, which can take the Chinese standard SI prefixes. In the engineering field, traditional units are rounded up to metric units.

Pinyin	Character	Relative value	Metric value	Imperial value	Notes
hū	忽		1 μm		Authorized name: 微米
sī	絲 or 丝		10 μm		Authorized name: 忽米
háo	毫		100 μm		Authorized name: 絲米 or 丝米
lí	釐 or 厘		1 mm		Authorized name: 毫米
fēn	公分		10 mm		Authorized name: 釐米 or 厘米
cùn	公寸		100 mm		Authorized name: 分米
chǐ	公尺	1	1 m		Authorized name: 米
Zhàng	公丈	10	10 m		Authorized name: 十米
yǐn	公引	100	100 m		Authorized name: 百米
lǐ	公里	1000	1000 m		this li is not the small li above, which has a different character and tone