Given concerns about the environmental impacts of fossil fuel use, there is a keen interest in developing a broad range of new energy sources and technologies. This in turn creates a need for metrics that can reliably quantify the costs, benefits, and potential trade-offs of different alternatives. In this paper, we present a definition of a full fuel-cycle metric that is flexible enough to describe a wide variety of energy production chains, and has sufficient mathematical rigor to allow meaningful comparisons between them. The term FFC (full fuel cycle) refers to the complete fuel production chain including extraction, processing, conveyance to the retail distribution center and delivery to final consumers. For ease of use in applications, the metric is defined as an FFC multiplier which, when applied to the point-of-use energy consumption, gives an estimate of the FFC energy use. We also show that the FFC multiplier can be used to provide precise and intuitively reasonable definitions of other energy production metrics such as EROI (energy return on energy invested). The multiplier is a non-linear function of a set of energy–intensity parameters that depend only on directly observable physical data.