Kalasin is a city located in northeast Thailand and serves as the capital of Kalasin Province. It is situated approximately 513 kilometres (319 miles) north-northeast of Bangkok by road.
The city covers the entirety of tambon Kalasin within the Mueang Kalasin District, spanning a total area of 16.96 square kilometres (6.55 square miles). As of 2015, the population of the city was recorded at 34,429.