The flag of Saint Helena, Ascension and Tristan da Cunha has an aspect ratio of 1:2. It consists of a Union Jack in the upper hoist-side quadrant, with the remaining area divided into three horizontal stripes – blue (#00247D) at the top, white (#FFFFFF) in the middle, and green (#007A3D) at the bottom. Centered on the right side of the flag is a shield from the Coat of Arms, which features a geometrically centered white-bordered shield split horizontally into two parts with the same colors as the aforementioned stripes.

The exact measurements or precise geometric properties of the flag aren't standardized, but the overall layout remains consistent across various versions of the flag.