The flag of Australia consists of a navy blue field with the Union Jack in the upper left corner, and a large seven-pointed white star known as the Commonwealth Star in the lower left corner. On the right half of the flag are five smaller white stars arranged in the shape of the Southern Cross constellation. The aspect ratio of the flag is 1:2, meaning it is twice as long as it is wide. The geometric properties are that the flag is rectangular with a width of 1 unit and a length of 2 units. The colors are specified in the Pantone Matching System (PMS) as follows:

• Blue: PMS 280 C
• Red: PMS 185 C
• White: PMS Safe
• Stars: PMS 285 C The size of the Union Jack is one quarter the length of the flag and its width is one third of the length of the Union Jack's widest part. The diameter of the large star is four-fifths the height of the Union Jack, and the stars of the Southern Cross have varying diameters based on their positions.