Length is a determining factor when selecting your arrows. An arrow that is too short can be dangerous, while an arrow that is too long can make you lose precision.
The ideal length for your arrows depends on your draw length. To find out your draw length, test out a bow. Take the bow in your hands and then, without using an arrow, standing in the shooting position. The distance between the string (where you would place the nock of your arrow) and the clicker (just beside the arrow rest) is your draw length. Ease the string back into its original position, without releasing it, in order not to damage the bow.
The ideal length of your arrow is your draw length plus 1 to 1.5 inches (2.5 to 4cm).
Decathlon recommends you do not choose arrows that are too short if there is a risk of your draw length increasing. The draw length of an archer who is still growing or developing can often increase rapidly.