The flag of the United Kingdom, also known as the Union Jack, has a blue background (#012169) with a red cross (St. George's Cross, #C8102E) over a white-bordered red diagonal cross (St. Patrick's Saltire, white #FFFFFF and red #C8102E) and a white diagonal cross (St. Andrew's Saltire, #FFFFFF).

Aspect ratio: 1:2

Geometric properties and measurements:

1. The width of the white St. Andrew's Saltire is 1/15 of the flag's height.
2. The width of the white border on the red St. Patrick's Saltire is 1/30 of the flag's height.
3. The width of the red St. Patrick's Saltire is also 1/15 of the flag's height (excluding the white border).
4. The width of St. George's Cross is 1/5 of the flag's height, with the red part 1/6 and the white fimbriation (border) 1/30 of the flag's height.

The Union Jack has no set dimensions for its various elements; they are specified as proportional to the flag's height as noted above.