Mumbai as seen from space. The island is clearly visible.

Mumbai spans an area 438 km² the city is on a peninsula on the island of Salcette. Because of this, the Mumbai (town) is often called the Island city. The city is spread linearly along the Arabian Sea coast. The city has a tropical climate with moderate to high levels of humidity. The moderating influence of the Arabian Sea ensures that there is very little fluctuation of seasonal temperatures. The warmest months of the year are March and October with temperature around 37-38 degrees Celsius. The coolest month is January with the day temperature around 26 degrees Celsius. It is also during this season that the city is enveloped with a thick layer of smog due to the inversion effect. Annual rainfall averages between 1.8 m and 2.4 m.

The city used to be seven hilly isles. When the isles were merged to form a monolithic island, these hills were razed and used to fill the shallows. Partly because of this, some parts of the city lie below sea level. Many parts of the city are still hilly. The highest point in the city is about 450 m and lies in the Powai-Kanheri range in the Borivali National Park. The city lies on a fault line and is earthquake prone (Zone 3 - up to a magnitude of 6.5). The geology of the area shows that the islands are composed of black basalt rock.

The city being adjacent to water, the temperature changes are not as drastic as those inland. Mumbai enjoys its monsoon showers from June to September with the annual rainfall being around 2.2 m (85 in). The city experiences light fog in the northern reaches of the city in Dec/Jan. Hailstones are rare. The lowest recorded temperature is 7 °C (45 °F) in 1962, the highest, 42 °C (108 °F). Temperatures (max/min) : Jan : 25/12 °C (77/54 °F) May : 35/28 °C (95/82 °F) July : 30/26 °C (86/79 °F) Oct : 38/23 °C (100/73 °F).