What is the «proportion», and which one is right for my flag?
The proportion is the ratio between the height and the width of the flag. The common one for a classic flag is 2:3. Every country has its own official proportion, which is not always 2:3.
A flag in proportion 2:3 is two units tall and three wide: 100x150cm, for example. A flag in 1:2 is twice as wide as it is tall: 100x200cm.
On the product page the line Sizes for proportion shows the proportion in use; Change opens the others.
Which one for a national flag?
Every country sets its own. Italy, France and Spain use 2:3. Slovenia, Croatia, Ireland and Hungary use 1:2.
When flags fly together, they follow the host country: the foreign flags take the proportion of the host's flag. In Italy that means 2:3 for every flag, so a Slovenian flag flown in Italy is ordered in 2:3, not in its official 1:2. In Slovenia, the Italian flag flying next to the Slovenian one would be 1:2. A flag flying alone in its own country keeps its official proportion.
For every European country's proportion and the etiquette behind the choice, read our blog article Flag proportions in Europe: which one to use, and why the host decides.