The coins, which were round with a square hole in the center, remained in circulation until 958 AD. These were the first of a series of coins collectively called jūnizeni or kōchō jūnisen (ja:皇朝十二銭).
"Wadōkaichin" is the transliteration of the four characters in the coin's inscription, which is thought to be composed of the era name Wadō (和銅, "Japanese copper"), which could alternatively mean "happiness", and "Kaichin", thought to be related to "Currency". This coinage was inspired by the (Chinese) Tang dynasty coinage (唐銭) named Kaigentsūhō (Chinese: 開元通宝, Kāiyuán tōngbǎo), first minted in Chang'an in 621 CE. The Wadōkaichin had the same specifications as the Chinese coin, with a diameter of 2.4 cm and a weight of 3.75 g.