Nepal measures about 880 kilometers (547 mi) along its Himalayan axis by 150 to 250 kilometers (93 to 155 mi) across. It has an area of 147,516 km² (56,956 sq mi).

Nepal is landlocked by China's Tibet Autonomous Region to the north and India on other three sides. West Bengal's narrow Siliguri Corridor separate Nepal and Bangladesh. To the east are Bhutan and India.

Nepal has a very high degree of geographic diversity and can be divided into three main regions: Terai, Hilly, and Himal. The Terai region, covering 17% of Nepal's area, is a lowland region with some hill ranges and is culturally more similar to parts of India. The Hilly region, encompassing 68% of the country's area, consists of mountainous terrain without snow and is inhabited by various indigenous ethnic groups. The Himal region, covering 15% of Nepal's area, contains snow and is home to several high mountain ranges, including Mount Everest, the world's highest peak. Nepal, with elevations ranging from less than 100 meters to over 8,000 meters, has eight climate zones from tropical to perpetual snow. The majority of the country's population resides in the tropical and subtropical climate zones. The tropical zone, below 1,000 meters, experiences frost less than once per decade and is suitable for growing various fruits and crops. The subtropical climate zone, from 1,000 to 2,000 meters, is the most prevalent and suitable for growing rice, maize, millet, wheat, and other crops. The temperate climate zone, from 2,000 to 3,000 meters, occupies 12% of Nepal's land area and is suitable for cold-tolerant crops. The subalpine, alpine, and nival zones have progressively fewer human settlements and agricultural activities.

Seasons are divided into a wet season from June to September and a dry season from October to June. The summer monsoon can cause flooding and landslides, while the winter monsoon is marked by occasional rainfall and snowfall. The diverse elevation results in various biomes, including tropical savannas, subtropical and temperate forests, montane grasslands, and shrublands.

Nepal has three categories of rivers: the largest systems (Koshi, Gandaki/Narayani, Karnali/Goghra, and Mahakali), second category rivers (rising in the Middle Hills and Lower Himalayan Range), and third category rivers (rising in the outermost Siwalik foothills and mostly seasonal). These rivers can cause serious floods and pose challenges to transportation and communication networks. River management involves addressing flooding, sedimentation, and sustainable water sources for irrigation. Building dams in Nepal is controversial due to seismic activity, glacial lake formation, sedimentation rates, and cross-border equity issues between India and Nepal.

Nepal's land cover is dominated by forests, which cover 39.09% of the country's total geographical area, followed by agriculture areas at 29.83%. The hill region constitutes the largest portion of Nepal, with significant cultivated lands and natural vegetation. Forests in Nepal face deforestation due to over-harvesting of firewood, illegal logging, clearing for agriculture, and infrastructure expansion. As of 2010, 64.8% of the forested area in Nepal is covered by core forests of more than 500 ha in size. Deforestation and degradation are driven by multiple processes, including firewood harvesting, construction, urban expansion, and illegal logging.

Nepal has consistently been ranked as one of the most polluted countries in the world.

For a country of its size, Nepal has tremendous geographic diversity. It rises from as low as 59 metres (194 ft) elevation in the tropical Terai—the northern rim of the Gangetic Plain, through beyond the perpetual snow line to 90 peaks over 7,000 metres (22,966 ft) including Earth's highest (8,848-metre (29,029 ft) Mount Everest or Sagarmatha). In addition to the continuum from tropical warmth to cold comparable to polar regions, average annual precipitation varies from as little as 160 millimetres (6.3 in) in its narrow proportion of the rainshadow north of the Himalayas to as much as 5,500 millimetres (216.5 in) on windward slopes, the maximum mainly resting on the magnitude of the South Asian monsoon.