Competition area
The competition area is a minimum of 14m x 14m and is divided into two zones. The inner zone called the contest area is a minimum of 8m x 8m to a maximum of 10m x 10m. The outer zone is the safety area and is a minimum of 3m wide.
The contest area is a different colour to the safety area.
When using two or more adjoining competition areas, the common or shared safety area is 4m.
A free zone, a minimum of 50cm, must be maintained around the entire competition area.
Tatamis
The competition area is covered by a Tatamis or similar material. The Tatamis is made of pressed foam and is 1m x 2m or 1m x 1m.
Platform
The platform is optional and is made of solid wood. It measures approximately 18m x 18m. When using a platform, it is recommended that the safety area is a minimum of 4m wide around the competition area.

References
International Judo Federation. Refereeing Rules 2014-2016 (PDF 155 KB)
Sport association details