Ranong is located on the Kra Isthmus, the narrow strip that connects mainland Thailand with the Malay Peninsula, on the west side of the Phuket mountain range. It has a long coast on the Andaman Sea. The province is known for having the most rainfall of all Thailand, the rainy season lasting for about eight months. In 1955 the annual rainfall reached 6,699.5 mm, compared to about 1,200 in central Thailand.
The province is the least populated province of Thailand; 80% of the area is covered by forests, and 67% is mountainous terrain. Historically the major industry was tin mining, but most mines are now exhausted. White clay mining for the production of porcelain and fishing are the main industries today, together with rubber and cashew nut farming.