Singapore consists of 63 islands, including the main island, widely known as Singapore Island but also as Pulau Ujong. There are two man-made connections to Johor, Malaysia: the Johor–Singapore Causeway in the north, and the Tuas Second Link in the west. Jurong Island, Pulau Tekong, Pulau Ubin and Sentosa are the largest of Singapore's smaller islands. The highest natural point is Bukit Timah Hill at 166 m (545 ft).

There are ongoing land reclamation projects, which have increased Singapore's land area from 581.5 km2 (224.5 sq mi) in the 1960s to 704 km2 (272 sq mi) today; it may grow by another 100 km2 (40 sq mi) by 2030. Some projects involve merging smaller islands through land reclamation to form larger, more functional islands, as with Jurong Island. 5% of Singapore's land is set aside as nature reserves. Urbanisation has eliminated most primary rainforest, Bukit Timah Nature Reserve being the only significant remaining forest.

Singapore has a tropical rainforest climate with no distinctive seasons, uniform temperature and pressure, high humidity, and abundant rainfall. Temperatures usually range from 23 to 32 °C (73 to 90 °F). Relative humidity averages around 79% in the morning and 73% in the afternoon. April and May are the hottest months, with the wetter monsoon season from November to January. From July to October, there is often haze caused by bush fires in neighbouring Indonesia. Although Singapore does not observe daylight saving time, it follows time zone GMT+8, one hour ahead of its geographical location.