The development of solid-gas thermochemical transformers requires the design and the construction of demonstration machines which could not exist without simulation models, allowing the dimensioning of fixed-bed solid-gas reactors. All of the models developed so far are based on a dynamic modelling of the process describing the temporal evolution of the principal elements of which the machine consists. This approach to dimensioning is certainly better adapted to the discontinuous and unstationary working mode of these machines. However, the dimensioning of the machine becomes a very complex and time consuming operation. With the aim of simplifying this procedure, some dimensioning nomograms have been developed in this study. They will enable any designer to draft a rapid dimensioning of a fixed-bed solid-gas reactor, thus facilitating decision making at the early stages of a project. These nomograms have been set up from a simplified analytical model which considers the average functional characteristics of a thermochemical reactor over a given time step. Finally, several applied examples are given to demonstrate the various possibilities, as well as the simple usage of these dimensioning nomograms.