All circles are measured by their diameter. A 20-meter circle, therefore, is a circle with a 20 meter diameter. The general circle sizes in dressage tests are: 20, 15, and 10 meters. Half-circles are incorporated in both training and test levels [an example is the “serpentine”]. Volte and Pessade are also variations of circles incorporated in higher levels of training.
The 20-meter circle is arguably one of the most important training figures in dressage and is seen from the most simple test (Intro in the USA) all the way to Grand Prix (highest level in FEI). The 20-meter circle is introduced early with green horses and beginner riders and becomes one of the go-to basics that grow your equestrian vocabulary.
15- and 10-meter circles require the horse to be more balanced and attentive so they are generally required later in training. The 15-meter circle is introduced in First-Level tests at the canter, while the 10-meter half-circle is introduced at the trot. The full 10-meter circle is not introduced into the dressage tests until Second Level, as is the 20-meter half-circle serpentine (“serpentine three equal loops, width of the arena, no change of lead” – 2011 Second Level, Test 1).
The Volte is a very small circle that is of a diameter less than 10 meters. While specifically defined as a diameter of 6 meters, trainers often vary the size of the volte dependent on the size, strength, and engagement level of the horse. While the volte is an excellent training tool, it is important not to push the horse to perform a smaller circle than is comfortable for them at the time.
The Pessade is a half-volte where the hindquarters are kept to the inside (making a smaller circle than the forehand). The pessade is used in training as a precursor to the pirouette when utilized at the walk and canter, and could be used to prepare a horse to move into Renvers. — MORE TO COME —
Quite often circles of varying sizes are incorporated into training for other purposes as well. For instance a trainer might utilize gradual decrease and increase of circle size from 20 meters down to 15 or even 12-meters to encourage the better use of the outside rein and outside leg independently responsible for controlling the shoulders (outside rein) and the body bend (outside leg prevents drifting and holds the bend), and then expand that work to encourage the horse to move away from the leg pressure to ‘yield’ in and then yield out of the circle, starting the process of “leg yield” in a horse in a fairly stress-free way.