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Who runs this site

The Hayami Tools Editorial Team, an individual operator. Contact details are on the Contact page.

How the site is made

The text and the tools on this site are written by an AI (Claude, by Anthropic), and approved by the operator before publication. Calculations are checked by automated tests against known values. For example, the Japanese holiday dates for the Japanese version of the site were compared, day by day from 1980 to 2027, against the list published by the Cabinet Office, with no differences.

Sources and data

• Shoe and clothing sizes follow the size charts published by a major Japanese marketplace, and the usual rules of thumb.
• Tatami sizes are the commonly used dimensions. The real estate figure (1.62 m² per jō) comes from the fair competition code for real estate advertising in Japan.
• Era dates are the start dates of each imperial era. The Gregorian calendar was adopted in Japan on January 1, 1873.

Please note

Results are approximate guides. For purchases, contracts and official procedures, check the exact figures with the shop, the maker or the relevant office. The operator is not responsible for any loss that comes from using this site.

Found a mistake?

Please tell us through the Contact page. We will check it and fix it.

Last updated: 2026-10-01