National Highway 81, commonly referred to as NH 81, is a highway connecting the city of Coimbatore to Chidambaram in South India. This highway was previously part of old national highways 67 and 227 but subsequent to rationalisation of national highway numbers of India by Gazette notification on 5 March 2010 it was changed to National Highway 81. This national highway is 321.4 km (199.7 mi) long and runs entirely in the Indian state of Tamil Nadu.