The flag of Saint Barthélemy features the coat of arms of the island on a white field. The aspect ratio of the flag is 2:3. The coat of arms consists of three parts: a blue chief, a red shield with gold fleurs-de-lis and a white Maltese cross, and a green terraced base.

To provide more detail without discussing symbolism:

Colors (approximate):

• Blue: Pantone 286C, Hex #0038A8
• Red: Pantone 1795C, Hex #DA291C
• Green: Pantone 347C, Hex #009E60
• Gold: Pantone 123C, Hex #FFC72C
• White: Hex #FFFFFF

Geometric properties and measurements:

1. White field - proportionally sized to match the flag's aspect ratio (width = 2x height).
2. Blue chief - the upper portion of the coat of arms occupying about 1/3 of the shield's height.
3. Red shield with gold fleurs-de-lis - main body of the shield forms the central part of the coat of arms, approximately 2/3 of the shield's height.
4. White Maltese cross - centered within the red shield.
5. Green terraced base - located below the red shield, occupying the lower third of the shield; its width matches the width of the shield.