Stone sculptures in royal tombs of the Joseon Dynasty were ritual objects whose kinds, forms, numbers, and dimensions were stipulated in ritual codes such as “Five Rites of King Sejong,” “Five Rites of the State,” and “Revised Edition on State Funerals.” Dimension regulations of stone sculptures changed according the period and sometimes specified minimal measures such as a “pun” (= 0.3 cm), which hardly made any difference in making actual sculptures. Nonetheless, this suggests that dimensions of stone sculptures were not randomly determined but calculated based on precise criteria. This article reconstructs the criteria for deciding dimensions of stone sculptures and their changes throughout the dynasty, focusing on the most representative stone sculptures of Joseon royal tombs, that is, seokin (stone figures of humans). First of all, the article identified the length of Yeongjo-cheok, which was the standard measure utilized in the regulations on sizes of stone sculptures in the royal tombs by actually checking the dimensions of the illustrations in the ritual codes such as “Five Rites of the State” and “Revised Edition on State Funerals.” Moreover, it investigated the development of the regulations based on “Formality of State Funerals,” “Five Rites of King Sejong,” “Five Rites of the State,” “Sequel to the Five Rites of the State,” and “Revised Edition on State Funerals,” and compared the regulations in different periods with actual stone sculptures installed in royal tombs. The first royal tomb of the Joseon Dynasty, Jeong-reung of Queen Shindeok, had been built according to the rules, designs, and scales of the tomb of King Gongmin of the Goryeo, before the regulations concerning stone sculptures in royal tombs were established in the Joseon Dynasty. A seokin in Jeong-reung is estimated as ten cheok (= 30.3 cm) long based on the size of the stone screen of Jeong-reung, which is currently built in the Gwangtong Bridge of the Cheonggye stream. King Taejong established the system of royal tombs during the construction of Geonwon-reung, which served as the standard for making the first funerary rules of the Joseon Dynasty, “Formality of State Funerals.” According to the funerary rules, the length of a seokin was to be seven cheok and five chon (= 3.03 cm). This length of a seokin was probably determined by deducting one forth of the entire length of a seokin in Jeong-reung from its original length. Subsequently, the sizes of a seokin became bigger based on “Five Rites of the State,” since a stone figure of a civil official and a stone figure of a military official were stipulated as eight cheok and three chon and nine cheok respectively in the new ritual code. The new sizes of the two types of stone figures were decided by adding one tenth of the entire length of a seokin in “Formality of State Funerals” to its original length and two tenth of that to the original respectively. In the following period, the constructions of royal tombs changed such as the disappearance of stone chambers and stone screens, and thus King Yeongjo revised the rules of stone sculptures accordingly. In the first version of the “Revised Edition on State Funerals” made in 1752, the sizes of a stone figure of a civil official and a stone figure of a military official were decided as five cheok, 1 chon and 1 pun, and five cheok and four chon respectively. The reason why the size of a stone figure of a civil official specified even the minimal length of 1 pun is because the size was determined according to the measurement of a stone sculpture in Hureung. In the revised version of “Revised Edition on State Funerals” made in 1758, the sizes of a stone figure of a civil official and a stone figure of a military official were made slightly bigger to be five cheok, eight chon and two pun, and six cheok and two chon respectively, according to the dimensions of the stone sculptures in Ui- reung of King Gyeongjong. Dimensions of stone sculptures for royal tombs of the Joseon Dynasty were not completely fixed but changed according to the circumstances of the period. They were usually decided based on those of the stone sculptures of the most important tombs at that time. However, the sizes of the “model” sculptures were not actually measured but derived from their dimensions recorded in the Royal Protocols, illustrating how the Joseon society regarded textual records as important. The rules of dimensions of stone sculptures in Joseon royal tombs were not enforced as laws but utilized as guidelines. Therefore, sizes of stone sculptures were adjusted based on the economic and political conditions at the time of construction of a royal tomb. For this reason, the stone sculptures of Joeson royal tombs came to have more rich history.