According to "Choya gunsai" (Collected Official and Unofficial Writings), the standard size was 36.36 centimeters in length, 8.18 in upper width, 7.27 centimeters in lower width, and 0.90 centimeters in thickness during the mid-Heian period.
『朝野群載』によれば、平安時代中期には長さ1尺2寸、上広2寸7分、下広2寸4分、厚さ3分が基準の大きさであった。