The United Kingdom is currently divided into 650 parliamentary constituencies, each of which is represented by one MP in the House of Commons. Although constituencies vary widely in area, the average number of voters in each constituency is approximately 68,175.
There are currently 533 constituencies in England, 59 in Scotland, 40 in Wales and 18 in Northern Ireland.
Largest and smallest constituencies
The largest constituency is Ross, Skye and Lochaber, measuring approximately 12,000 square kilometres.
The smallest constituency is Islington North, measuring 7.35 square kilometres.
Parliamentary constituency boundaries
Constituency boundaries are kept under review by four permanent Boundary Commissions, one each for England, Scotland, Wales and Northern Ireland.
The Commissions make reports at regular intervals, usually every 5 years, recommending any necessary changes due to population change or changes in local government boundaries.
Any changes must be agreed by both Houses of Parliament.
House of Commons Library analysis
The House of Commons Library produces briefing papers to inform MPs and their staff of key issues. The papers contain factual information and a range of opinions on each subject, and aim to be politically impartial.
The Library has published papers on the Fifth and Sixth Periodical Reviews of Parliamentary Constituency Boundaries.
Select Committee inquiry
MPs on the Political and Constitutional Reform Select Committee are carrying out an inquiry on 'What next on the redrawing of Parliamentary boundaries?'
Find out more about the inquiry:
You can find out what constituency you are in, and the MP who represents that constituency, by using the Find your MP service.