Green chemistry metrics measures efficiency in a chemical process. Having made a Green Chemistry improvement to a chemical process, it is important to be able to quantify the change. By quantifying the improvement, there is a tangible element or benefit from the new technology introduced. This is likely to aid the communication of the work and potentially facilitate the transfer to industry. For yield improvements and selectivity increases, simple percentages are suitable, but this simplistic approach may not always be appropriate. For example, when a highly pyrophoric reagent is replaced by a benign one, a numerical value is difficult to assign but the improvement is obvious, if all other factors are similar.

Numerous metrics have been formulated over time and their suitability discussed at great length.

The problem observed is that the more accurate and universally applicable the metric devised, the more complex and unemployable it becomes. A good metric must be clearly defined, simple, measurable, objective rather than subjective and must ultimately drive the desired behavior.