Собственная работа. Geometry and dimensions from Ley no 42 "de los Símbolos Nacionales".

Its shape is rectangular, twice length than width, composed by five horizontal stripes having all the same width, three deep blue and two white, placed alternating. A red equilateral triangle, in one of its vertical extremes occupy all the height of the flag constituting its fixed edge. Such triangle bears in its center a five-pointed white star, within an imaginary circumference, whose diameter is a third of the flag´s height, having one of its points towards the free upper edge of the flag.

— English translation of Law 42 from Symbols of the Cuban Nation