In dressage, the strategically positioned letters within the arena play a crucial role in guiding riders through their routines. Each letter corresponds to a specific reference point for executing movements, transitions, and figures with precision. This helps riders follow the correct path while riding tests or when having a lesson with a trainer. Furthermore, during tests, these letters serve as aids for the judges to consistently evaluate performances across various riders and horses.

You usually find two types of dressage arenas: a standard, smaller one, and a slightly larger arena. The size of an arena for a dressage show can vary, with the larger arena being more common, especially on the higher levels.

The smaller dressage arena is 20 meters by 40 meters. 8 letters are used around the edge of the arena, and 3 imaginary letters down the center line.  

While the larger dressage arena has the same width, it is significantly longer:  20 meters by 60 meters, with 12 letters around the edge of the arena and 5 along the imaginary center line.  

Check out these two illustrations for the proper layout and spacing of arena letters, both for 20x40m and 20x60m dressage arenas.

You can download the illustrations here and here.