Which national flag is square rather than rectangular?

Switzerland’s national flag is square rather than rectangular.

The Swiss flag has a white Greek cross centered on a red square field. Its arms are equal in width, and the cross is slightly shorter than the flag’s height and width, according to official construction rules.

Switzerland is one of only two sovereign states whose national flags are square in their standard form; the other is Vatican City. Swiss civil and state flags are square, while the Swiss ensign used at sea has a rectangular proportion.

The design developed from military cantonal banners and became a national symbol in the nineteenth century. It is often confused with the Red Cross emblem, but the Red Cross reverses the colors: a red cross on a white field.