An important facet of developing engineering design concepts is the ability to promptly and accurately project the total constructed cost of a given device concept, since these cost projections are important factors for future decisions on project scope. In order to provide a credible and consistent means for projecting the total constructed cost of a given device or reactor concept, an automated approach to performing and cataloging cost estimates has been developed at the Fusion Engineering Design Center (FEDC), wherein the cost estimate record is stored in the LOTUS 1-2-3† spreadsheet on an IBM† personal computer. The cost estimation spreadsheet is based on the cost coefficient/cost algorithm approach to cost estimating and incorporates a detailed generic code of cost accounts for both tokamak and tandem mirror devices. Component design parameters (weight, surface area, etc.) and cost factors are input, and direct and indirect costs are calculated. The cost data base file derived from actual cost experience within the fusion community and refined to be compatible with the spreadsheet costing approach is a catalog of cost coefficients, algorithms, and component costs arranged into data modules corresponding to specific components and/or subsystems. Each data module contains engineering, equipment, and installation labor cost data for different configurations and types of the specific component or subsystem. This paper describes the assumptions, definitions, methodology, and architecture incorporated in the development of the cost estimation spreadsheet and cost data base, along with the type of input required and the output format.