Bulgaria occupies a portion of the eastern Balkan peninsula, bordering five countries — Greece and Turkey to the south, Macedonia and Serbia to the west, and Romania to the north. The land borders have a total length of 1,808 kilometres (1,123 mi), and the coastline has a length of 354 kilometres (220 mi). Its total area of 110,994 kilometres (68,968 mi) ranks it as the world's 105th-largest country. Bulgaria's geographic coordinates are 43° N 25° E.

The most notable topographical features are the Danubian Plain, the Balkan Mountains, the Thracian Plain, and the Rhodope Mountains. The southern edge of the Danubian Plain slopes upward into the foothills of the Balkans, while the Danube defines the border with Romania. The Thracian Plain is roughly triangular, beginning southeast of Sofia and broadening as it reaches the Black Sea coast.

The Balkan mountains run laterally through the middle of the country. The mountainous southwest of the country has two alpine ranges—Rila and Pirin, which border the lower but more extensive Rhodope Mountains to the east. Bulgaria is home to the highest point of the Balkan peninsula, Musala, at 2,925 metres (9,596 ft) and its lowest point is sea level. Plains occupy about one-third of the territory, while plateaus and hills occupy 41 per cent. The country has a dense network of about 540 rivers, most of which are relatively small and with low water levels. The longest river located solely in Bulgarian territory, the Iskar, has a length of 368 kilometres (229 mi). Other major rivers include the Struma and the Maritsa in the south.

Bulgaria has a dynamic climate, which results from its being positioned at the meeting point of Mediterranean and continental air masses and the barrier effect of its mountains. Northern Bulgaria averages 1 °C (1.8 °F) cooler and registers 200 millimetres (7.9 in) more annually than the regions south of the Balkan mountains. Temperature amplitudes vary significantly in different areas. The lowest recorded temperature is −38.3 °C (−36.9 °F), while the highest is 45.2 °C (113.4 °F). Precipitation averages about 630 millimetres (24.8 in) per year, and varies from 500 millimetres (19.7 in) in Dobrudja to more than 2,500 millimetres (98.4 in) in the mountains. Continental air masses bring significant amounts of snowfall during winter.