The Flag of Switzerland consists of a red square with a bold, equilateral white cross in the center. It is one of only two square sovereign-state flags, the other being the flag of the Vatican City. (The civil and state ensign, used by Swiss ships and boats, has more traditional proportions of 2:3.)

Only the dimensions of the cross are formally established since 1889: "The coat of arms of the federation is, within a red field, an upright white cross, whose [four] arms of equal length are a sixth longer than their width.". The size of the cross in relation to the field is not formally established except on the naval ensign. A relation of 2:3 or 7:10 to the span of the flag is usual.