Own work. Geometry and dimensions from Government of Iceland — Icelandic National Flag and Act on of the National Flag of Icelanders and the Coat of Arms.

The Government, Parliament and other official institutions, as well as representatives of the Ministry responsible for foreign affairs abroad, shall use a swallowtail flag. The swallowtail flag differs from the regular National Flag in that its fly end sections are three times the length of the hoist sections, with the fly end cut along straight lines drawn from its corners towards its centre line to intersect the inside border between the fly end sections. These lines intersect the inner edges of the fly end sections at the point where 4/7 of their outer length and 3/7 of their inner length meet. The red cross is cut perpendicularly where these lines meet its arm.

— Article 2 of the Flag Act No. 34/1944