This document proposes a formal definition of disentangled representations and new evaluation metrics. It defines disentangled representations as having three key properties: informativeness, separability, and interpretability. Mathematical formulas are provided for these properties. Two new metrics are proposed to measure separability and interpretability in both supervised and unsupervised settings. The metrics aim to overcome limitations of prior work by not requiring knowledge of all ground truth factors or additional training. Experiments applying the new metrics to models are referenced but not described in detail.