The Protein Efficiency Ratio (PER) is a measure for the bodyweight increase that can be achieved per unit of protein intake.
Equation
\[\text{PER} = {\Delta W \over \text{CP}_{f} \sum_{i=1}^{t}m_{f}} = {W_{2} – W_{1} \over \text{CP}_{f} \sum_{i=1}^{t}m_{f}}\] with \(\Delta W\) describing the difference between final (\(W_{2}\)) and initial (\(W_{1}\)) bodyweight in gram, \(\text{CP}_{f}\) denoting for the relative crude protein content of the feed and \(m_{f}\) being the amount of feed fed in gram during the experimental period \(t\) in days. This can be written in a more simplistic way as follows: \[\text{PER} = {\text{AG} \over \text{GP}}\] with \(\text{AG}\) representing the absolute growth and \(\text{GP}\) describing the gross protein intake.