Abstract Construction of spherical vessel in various dimensions is known as one of the frequent problems for construction and production engineers, since conventional methods of shell construction require mold and press which leads to higher costs of production. Therefore, current work has tried to investigate a new method based on explosive forming without using molds. In this technique, final shape of the shell can be achieved by explosion inside a prefabricated structure called four cones. This structure is produced from combination and welding of four truncated cones two of which are paired in each side. Initial shape of the tank is then used to transform this structure into a more complete sphere using explosives at its center. This paper aims to study the amount of explosives needed for this process in terms of vessel’s diameter and thickness. In this regard, simulation was run by LS-DYNA software and the resultant outputs were evaluated with those of experimental tests. The results shows that the required charge of forming varies exponentially with thickness.