Sumo and the Dohyo (Sumo ring)Archived September 28, 2007, at the Wayback Machine Nobuhiko Tsunefuka, 'The dohyo of the Edo period had a diameter of 13 shaku (3 m, 94 cm) and this size was enlarged by 61 centimeters at an Emperor’s Sumo match on April 29, 1931 to the current diameter of 15 shaku (4 m, 55 cm)'
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Sumo and the Dohyo (Sumo ring)Archived September 28, 2007, at the Wayback Machine Nobuhiko Tsunefuka, 'The dohyo of the Edo period had a diameter of 13 shaku (3 m, 94 cm) and this size was enlarged by 61 centimeters at an Emperor’s Sumo match on April 29, 1931 to the current diameter of 15 shaku (4 m, 55 cm)'
