Modular plant design is an approach for making chemical production more flexible and more efficient. Different approaches for modular plant design have been developed, for example in the CoPIRIDE or F-3 factory project. They have in common that reductions in design and construction expenses for modular equipment and its assembly are expected e.g. by preassembly of modules in a workshop under controlled conditions resulting in less field work on the construction site for erection. However, the main disadvantage of the modular approach is the loss of economy of scale. Thus, the effective impact of the modular concept concerning the fixed capital investment has to be investigated. In this article, a new approach for estimating fixed capital investment of modular production plants will be presented and applied using a generic example. Based on the results we expect that positive effects through modularization on engineering and construction costs can nearly compensate the loss of economy of scale. In the investigated example investment costs of the modular plant are 12% higher than for the comparable conventionally built plant. Such increase could allow other effects that are attributed to the modular concept to be employed to advantage. That would be an economic improvement and a reduction of investment risk in view of the modular plant's life cycle.