Flags are usually rectangular in shape (often in the ratio 2:3, 1:2, or 3:5), but may be of any shape or size that is practical for flying, including square, triangular, or swallow tailed. A more unusual flag shape is that of the flag of Nepal, which is in the shape of two stacked triangles. Other unusual flag shapes include the flag of Ohio and the flag of Tampa.
Many flags are dyed through and through to be inexpensive to manufacture, such that the reverse side is the mirror image of the obverse(front) side, generally the side displayed when the flag is flying from the observer's point of view from left, the side of the pole, to right. This presents two possibilities:
If the design is symmetrical in an axis parallel to the flag pole, obverse and reverse will be identical despite the mirror-reversal, such as the Indian Flag or Canadian Flag
If not, the obverse and reverse will present two variants of the same design, one with the hoist on the left (usually considered the obverse side, the other with the hoist on the right (usually considered the reverse side of the flag). This is very common and usually not disturbing if there is no text in the design.
Some complex flag designs are not intended for through and through implementation, requiring separate obverse and reverse sides if made correctly. In these cases there is a design element (usually text) which is not symmetric and should be read in the same direction, regardless of whether the hoist is to the viewer's left or right. These cases can be divided into two types:
The same (asymmetric) design may be duplicated on both sides. Such flags can be manufactured by creating two identical through and through flags and then sewing them back to back, though this can affect the resulting combination's responsiveness to the wind. Depictions of such flags may be marked with the symbol , indicating the reverse is congruent to (rather than a mirror image of) the obverse.
Rarely, the reverse design may differ, in whole or in part, from that of the obverse. Examples of flags whose reverse differs from the obverse include the flag of Paraguay, the flag of Oregon, and the historical flag of the Soviet Union. Depictions of such flags may be marked with the symbol .
Common designs on flags include crosses, stripes, and divisions of the surface, or field, into bands or quarters—patterns and principles mainly derived from heraldry. A heraldic coat of arms may also be flown as a banner of arms, as is done on both the stateflag of Maryland and the flag of Kiribati.
The de jure flag of Libya under Muammar Gaddafi, which consisted of a rectangular field of green, was for a long period the only national flag using a single colour and no design or insignia. However, other historical states have also used flags without designs or insignia, such as the Soviet Republic of Hungary, whose flag was a plain field of red.
Colours are normally described with common names, such as "red", but may be further specified using colorimetry.
The largest flag flown from a flagpole worldwide, according to Guinness World Records, is the flag of Mexico flown in Piedras Negras,Mexico. This flag was about 2,058 m2 (22,150 sq ft).The largest flag ever made was the flag of Qatar; the flag, which measures at 101,978 m2 (1,097,680 sq ft), was completed in December 2013 in Doha.