Mae Hong Son Province is situated in northern and northwestern Thailand at 17° 38′ - 19° 48′ N and 97° 20′ - 98° 39′ E and furthest from Bangkok in the north at a distance of approximately 924 km. It boasts an area of approximately 12,681.259 km² or around 7,925,812.5 rai, which is third largest in Northern Thailand and seventh largest in the country. It is approximately 250 km from north to south and approximately 95 km from east to west.
To the north and west it connects to a total of three states in the Union of Burma, namely the southern portion of Shan State; Kayah State and Kawthoolei State via the West Thanon Thongchai Mountains and the rivers Salween and Moei which serve as natural boundaries between the countries. To the south it connects to the district of Tha Song Yang, Tak via the rivers Yuam and Ngao which serve as a provincial boundary. To the east it connects to the districts of Wiang Haeng, Chiang Dao, Mae Taeng, Mae Chaem, Hot and Omkoi in Chiang Mai Province via the Central and East Thanon Thongchai mountain ranges that serve as a boundary line between the two provinces.
Every district in Mae Hong Son Province shares a common border with the Union of Burma approximately 483 kilometres in total length. Of this, approximately 326 kilometres is land and 157 kilometres are rivers (not counting the Salween, 127 km, and Moei, 30 km)