Kirn is a town in the Bad Kreuznach district in Rheinland-Pfalz, Germany. It is the seat of the Verbandsgemeinde Kirner Land. Kirn is a middle centre serving an area on the Nahe and in the Hunsrück.
Kirn lies in a landscape characterized by the Nahe valley and the valley of the Hahnenbach, cut deeply into the Lützelsoon, roughly 10 km northeast of Idar-Oberstein and 30 km west of Bad Kreuznach. The valley floors are heavily settled in places, whereas the steep slopes in the higher areas are mostly bare of buildings and decked with forest. Rising up above the woodland canopy in many places are freestanding quartzite crags. Particularly striking among these are the Oberhauser Felsen, the Kallenfels and the Wehlenfelsen north of the town. Flowing through the unhurried inner town is the Hahnenbach, which rises in the Hunsrück, and not too much farther downstream empties into the Nahe. Also characterizing the town's appearance is the quarry up from the town centre, which stretches eastwards all the way to the town limit.
Kirn's municipal area measures 16.53 km2, and by percentages, the uses of this land break down thus:
Agriculture — 15.1
Woodland — 51.9
Open water — 2.4
Residential and transport — 28.6
Other — 2.0
Clockwise from the north, Kirn's neighbours are the municipalities of Oberhausen bei Kirn, Hochstetten-Dhaun, Meckenbach, Heimweiler and Bärenbach, the town of Idar-Oberstein and the municipalities of Fischbach, Bergen and Hahnenbach. Idar-Oberstein, Fischbach and Bergen all lie in the neighbouring Birkenfeld district, whereas all the others likewise lie within the Bad Kreuznach district.
Kirn's Stadtteile are the main centre, also called Kirn, and the two outlying centres of Kallenfels and Kirn-Sulzbach. Also belonging to Kirn are the outlying homesteads of Akvas Papiermühle, Cramersmühle, Füllmannsmühle, Hasenfels, Kallenfelser Hof, Kyrburg, Ölmühle Spielmann and Schleif-Mühle.
Yearly precipitation in Kirn amounts to some 540 mm, which is rather low, falling below average for the precipitation chart for all Germany.