The Only Non-Rectangular National Flag (and Other Oddities)

Nepal's flag is the single exception to "every national flag is a four-sided shape," full stop. It's made of two stacked, pointed pennants (crimson red, with a blue border), rather than any kind of quadrilateral — a shape called a double pennant. The design dates back centuries as a combination of two separate royal or Rana-family pennants that were formally merged into one national symbol; the modern version, including its precise geometric construction (the flag is defined by a mathematical formula in Nepal's constitution rather than a simple template, specifying exact angles and proportions), was standardized in 1962. The white moon-and-sun emblems on the two pennants were simplified from more elaborate crescent-and-face designs in that same 1962 standardization, partly to make the flag easier to reproduce accurately.

Because Nepal's shape is so unusual, it also makes the flag one of the very few national flags that's genuinely difficult to mistake for any other — most flag confusion pairs, discussed in the most confused flag pairs on Earth, come down to shared colors or layouts precisely because nearly every other flag is competing within the same rectangular template.

Two sovereign states fly perfectly square flags rather than rectangular ones: Switzerland and Vatican City. Switzerland's white cross on a red square field has roots in medieval Swiss cantonal war banners, which were traditionally square; the country formally fixed the square proportion (rather than any specific rectangle) when it adopted its current flag design in the mid-19th century, and it has remained square ever since even as most of the rest of the world standardized on rectangles. (Switzerland's civil ensign, flown by ships, is actually a rectangle — a wrinkle covered in the national flag vs. civil ensign guide, since maritime signal conventions generally require a longer rectangular shape for visibility at sea.) Vatican City's flag, adopted in 1929 when the Vatican became a sovereign state, was deliberately designed as a square to visually echo Switzerland's, given the historical link between the two — the Swiss Guard has protected the Pope since the 16th century.

A separate, smaller category of flags keep the overall rectangle but cut a V-shaped notch into the fly end (the edge farthest from the pole), producing a swallowtail or pennant-style silhouette. This convention has military and naval roots — a swallowtail cut was historically used to distinguish a command or signal flag from an ordinary rectangular one at a glance, even from a distance where the full design wasn't legible. Ohio's US state flag is the best-known modern example of a swallowtail, though as a state flag rather than a national one it falls outside the strict "national flags" scope of the non-rectangular list linked above; several historical and naval ensigns across different countries have used the same cut for the same signaling reason.

A separate category worth distinguishing from true non-rectangular flags is the small group of rectangular flags with a genuinely unusual internal geometry rather than an unusual outer silhouette. The diagonals-and-triangles feature list covers these — flags like Saint Kitts and Nevis or the Democratic Republic of the Congo, which use a diagonal band or corner triangle instead of the far more common horizontal or vertical stripe layout. These stay rectangular in overall shape, but the internal design breaks from the stripe-and-canton template just as deliberately as a swallowtail cut breaks from the outer edge, usually for the same underlying reason: making the flag instantly recognizable against a field of otherwise similar rectangles.

The practical case against a non-rectangular national flag is straightforward: manufacturing, shipping, and displaying a flag gets meaningfully more complicated once it isn't a simple standardized rectangle, and a flag that has to fly correctly on everything from a schoolhouse pole to a warship's mast benefits enormously from being interchangeable with every other flag in the world in terms of hardware and hoisting method. Nepal's flag is the clearest proof that the exception is possible when a country's design tradition predates the rectangle becoming a near-universal default and the country chooses to keep it anyway rather than modernize it away, as several other historically pennant-shaped regional banners quietly did over the centuries. For how a flag's overall design is judged more broadly — shape included — the guide to how flags are designed covers the North American Vexillological Association's five core principles, one of which (simplicity) is part of why the rectangle convention is so durable in the first place.