Lithuania is located in the Baltic region of Europe[a] and covers an area of 65,200 km2 (25,200 sq mi). It lies between latitudes 53° and 57° N, and mostly between longitudes 21° and 27° E (part of the Curonian Spit lies west of 21°). It has around 99 kilometres (61.5 mi) of sandy coastline, only about 38 kilometres (24 mi) of which face the open Baltic Sea, less than the other two Baltic Sea countries. The rest of the coast is sheltered by the Curonian sand peninsula. Lithuania’s major warm-water port, Klaipėda, lies at the narrow mouth of the Curonian Lagoon (Lithuanian: Kuršių marios), a shallow lagoon extending south to Kaliningrad. The country’s main and largest river, the Nemunas River, and some of its tributaries carry international shipping.

Lithuania lies at the edge of the North European Plain. Its landscape was smoothed by the glaciers of the last ice age, and is a combination of moderate lowlands and highlands. Its highest point is Aukštojas Hill at 294 metres (965 ft) in the eastern part of the country. The terrain features numerous lakes (Lake Vištytis, for example) and wetlands, and a mixed forest zone covers over 33% of the country. Drūkšiai is the largest, Tauragnas is the deepest and Asveja is the longest lake in Lithuania.

After a re-estimation of the boundaries of the continent of Europe in 1989, Jean-George Affholder, a scientist at the Institut Géographique National (French National Geographic Institute), determined that the geographic centre of Europe was in Lithuania, at 54°54′N 25°19′E, 26 kilometres (16 mi) north of Lithuania’s capital city of Vilnius. Affholder accomplished this by calculating the centre of gravity of the geometrical figure of Europe.