The flag of Saint Lucia has an aspect ratio of 1:2. It consists of a blue field (Pantone 286C) with a yellow isosceles triangle (Pantone 116C) in the center, which is based on the width of the flag and extends from the lower hoist-side corner to the upper fly-side corner. The yellow triangle is bordered by two white (Pantone White) and black (Pantone Black) triangles, each having a width equal to 1/48th of the flag's width.

The flag's geometric properties are as follows:

1. The blue field covers the entire flag.
2. The yellow triangle has its base along the entire width of the flag at the hoist side and its apex at the opposite corner on the fly side.
3. The white and black triangles form a border around the yellow triangle, with the white triangle being closer to the yellow triangle and the black triangle being outermost.

All measurements are proportional to the flag's width and length.