The flag of the United Kingdom, also known as the Union Jack, has an aspect ratio of 1:2. It consists of a blue field with a diagonal red cross, which represents Saint Patrick, the patron saint of Ireland, and a diagonal white cross, which represents Saint Andrew, the patron saint of Scotland. In the center of the flag, there is a white outlined red cross, which represents Saint George, the patron saint of England.

The color codes for the Union Jack are:

• Blue: Pantone 280 C / CMYK (100, 72, 0, 18) / RGB (0, 33, 71) / Hex #00247D
• Red: Pantone 186 C / CMYK (0, 100, 81, 4) / RGB (206, 17, 38) / Hex #CE1126
• White: No Pantone code / CMYK (0, 0, 0, 0) / RGB (255, 255, 255) / Hex #FFFFFF

The width of each arm of the cross is 1/5 of the flag's width, while the thickness of the lines is 1/15 of the flag's width. The exact measurements of the flag may vary depending on its use, but it is typically flown in sizes ranging from 3 feet by 6 feet to 20 feet by 40 feet.

Geometrically, the flag can be divided into four equal rectangles, with two of them forming a larger upright rectangle and the other two forming a smaller one. The diagonals of the smaller rectangle are perpendicular to those of the larger one.

Note: It's worth noting that the flag of the United Kingdom is different from the flags of England, Scotland, Wales, and Northern Ireland, which have their own distinct designs.