The kos, also spelled coss, koss, kosh, koh(in Punjabi), krosh, and krosha, is a unit of measurement which is derived from a Sanskrit term, क्रोश krośa, which means a 'call', as the unit was supposed to represent the distance at which another human could be heard. It is an ancient Indian subcontinental standard unit of distance, in use since at least 4 BCE. According to the Arthashastra, a krośa or kos is about 3000 m. Another conversion is based on the Mughal emperor Akbar, who standardized the unit to 5000 guz in the Ain-i-Akbari. The British in India standardized Akbar's guz to 33 in, making the kos approximately 4191 m. Another conversion suggested a kos to be approximately 2 English miles.

Arthashastra Standard units

The "Arthashastra: Chapter XX. "Measurement of space and time", authored in 4th century BC by Chanakya (Vishnugupta Kauṭilya), sets this standard breakup of Indian units of length:

Conversion to SI units and imperial units

Kos may also refer to roughly 1.8 km Arthashastra standard unit of kos or krosha is equal to 3075 metres in SI units and 1.91 miles in imperial units.

Usage of kos

Evidence of official usage exists from the Vedic period to the Mughal era. Elderly people in many rural areas of the Indian subcontinent still refer to distances from nearby areas in kos. Most Hindu religious Parikrama circuits are measured in kos, such as 48 kos parikrama of Kurukshetra. Along India's old highways, particularly the Grand Trunk Road, one still finds 16th to early 18th century Kos Minars, or mile markers, erected at distances of a little over two miles.