The flag of the British Indian Ocean Territory (BIOT) has an aspect ratio of 1:2. It features a blue field with the Union Jack in the canton and the BIOT coat of arms in the fly.

Color codes:

• Blue (Pantone 300): #012169
• Red (Pantone 186): #C8102E
• White: #FFFFFF

The Union Jack occupies the upper hoist-side quadrant, with its dimensions being half the width and height of the flag. The BIOT coat of arms is centered in the right half of the flag, with its height being 3/5 of the flag's height and positioned equidistant from the top, bottom, and fly edges.