You will need:

A flat location slightly larger than the arena you want to make.
Allow for an extra 1-2 metres all round so that you have room to place your markers a little way back from the sides of your arena.

Markers for the corners and sides of the arena.

For the corners you could use posts or stakes if you want to make a more permanent arena or something like jump wings, upturned buckets or cones for a temporary arena.
For the sides of the arena you could use fencing, jump poles or ropes laid on the ground.
Most tack shops can supply ready-made dressage boards to mark out an arena.

You could use upturned buckets or cones with the letters painted on or make your own markers from off-cuts of wood. You can also buy ready-made markers.

If you don’t have a long enough tape measure you could use a ball of string and mark it off in metres with a marker pen or you could hire a trundle wheel or a long tape measure from most hire shops.

Using the measurements in the diagram below for the size of arena you want to make, place your markers at the corners of the arena.
To check that your arena is square measure the long diagonals and make sure that they are the same as each other.
It’s not essential but it will help you to ride a straight line if you can mark the sides of the arena. Make sure that you have left space to enter along the long side, e.g. at K or at F.
Next place your dressage markers using the diagrams for reference. Make sure that each pair of markers is opposite each other and that all the letters can be clearly seen if you stand at C.

20 x 40 arena	20 x 60 arena