It is well known that the Dutch East India Company (Verenigde Oostindische Compagnie) conducted trade with Japan during the 17th and 18th centuries. In 1609, the company established a factory in Hirado, which in 1641 was ordered to move to Nagasaki. In both factories, the Dutch merchants kept their account books according to the Italian system of double-entry bookkeeping. These account books-for example, the journals (Negotie Journalen) and the ledgers (Negotie Grootboeken)-are preserved in the Netherlands National Archives in The Hague. In the past, Oskar NACHOD and Japanese scholars have made use of these archival materials for their analyses of the management of the Dutch factory in Japan. However, because they did not entirely understand the bookkeeping system used, the results of their calculations for the volume of trade are not precise, and their results differ from each other. This paper tries to clarify how to calculate the actual figures of import and export goods for Japanese-Dutch trade by analysing the account books in the first half of the 17th century. It also seeks to correct the results of the calculations by NACHOD and others. During this period, Japanese-Dutch trade experienced transitions in scale and formation due to the foreign and trade policies of both sides and the situation on the high seas and coastal waters of East and Southeast Asia. The account books are fundamental archival sources, and they provide a detailed picture of the annual trade between Japan and the Dutch East India Company. However, we cannot understand the exact volume recorded unless we have a clear idea of the way in which the books were organized.