The Hogetsu's amount of 0.6270 sho is calculated with the standard kane-jaku (a carpenter's iron square) which was used commonly in medieval Japan, however "Irohajirui-sho" was compiled by the late Heian period at the latest when ritsuryo-jaku (the length measure established under the Ritsuryo system) was 0.97 times of the length of the kane-jaku, that is, it was 0.5722 sho in present day.
ただ、寶月による0.6270も尺度を中世に普遍的に使われた曲尺として計算しているが、『伊呂波字類抄』は遅くとも平安末期には成立していたので、律令尺は、曲尺の0.97に当たるので現升の0.5722升に当たるものと推定される。