Number + 公里
公里 (gōnglǐ) is the standard Chinese measure word for "kilometer," used to express distance or speed. It appears after a number, as in 30 公里 (30 kilometers), and in speed expressions like 30 公里/小时 (30 km/h). It is the metric equivalent of the traditional Chinese unit 里.
从这里到机场大约有三十公里。
Cóng zhèlǐ dào jīchǎng dàyuē yǒu sānshí gōnglǐ.
It's about thirty kilometers from here to the airport.
我每天跑步五公里来保持身体健康。
Wǒ měitiān pǎobù wǔ gōnglǐ lái bǎochí shēntǐ jiànkāng.
I run five kilometers every day to stay healthy.
这条高速公路限速一百二十公里每小时。
Zhè tiáo gāosù gōnglù xiànsù yībǎi èrshí gōnglǐ měi xiǎoshí.
This expressway has a speed limit of one hundred and twenty kilometers per hour.