The Feed Conversion Ratio (FCR) is a simple indicator of the conversion efficiency of the given feed into biomass. However, the practical use of the FCR is described as limited because it allows a comparison only based on the absolute amount of feed eaten, but not for the amount of nutrients delivered with the feed (Fry, 2018).
Equation
\[\text{FCR} = {\text{F} \cdot \text{DM} \over \Delta W}\] with \(\text{F}\) denoting the feed intake in gram per individual multiplied by the \(\text{DM}\) content of the feed in percent, and \(\Delta W\) denoting for the weight gain per individual in gram over the observed time period.
References
Fry, J. P., Mailloux, N. A., Love, D. C., Milli, M. C., & Cao, L. (2018). Feed conversion efficiency in aquaculture: do we measure it correctly? Environmental Research Letters, 13, 24017.