The island of Ireland lies off the north-west coast of the continent of Europe between 51½° and 55½° north latitude and 5½° and 10½° west longitude.

The Irish Sea to the east, which separates Ireland from Britain, is from 17.6 to 192 kilometres (11 to 120 miles) wide and has a maximum depth of about 200 metres (650 feet). Around the other coasts the shallow waters of the Continental Shelf are rather narrow and depths increase rapidly into the Atlantic Ocean.

The total area of Ireland is 84,421 square kilometres (32,595 square miles). Ireland (Republic) comprises 70,282 square kilometres (27,136 square miles) and Northern Ireland 14,139 square kilometres (5,459 square miles). The greatest length of the island from north to south is 486 kilometres (302 miles) and the greatest width, from east to west, is 275 kilometres (171 miles). There are 5,631 kilometres of coastline (3,500 miles).

The island comprises a large central lowland of limestone with a relief of hills and a number of coastal mountains, the highest of which, Carrantuohill, is 1,040 metres (3,414 feet). The Shannon is the longest river 340 kilometres (230 miles). There are many lakes of which Lough Neagh, 396 square kilometres (153 square miles), is the largest.