(a) providing a computer implemented checklist including various items related to components and/or current observed conditions of a compressed air system, the compressed air system including a supply side and a demand side, the supply side including equipment in or near compressor room(s), the demand side including at least one process or production end use, the checklist further including, for each component and/or current observed condition two or more values that correspond to two or more possible conditions, the values being weighted to represent the respective impact of the current observed condition on the estimated efficiency of the compressed air system;

(b) manually observing a compressed air system to determine the current observed condition for each item in the checklist;

(c) selecting the closest value for each item from the two or more values in the checklist by comparing, for each item, the current observed condition with the set of possible conditions listed in the checklist and assigning the value associated with the condition that is the closest match to the current observed condition, and when it is determined that the current observed condition for an item lies between two of the possible conditions listed in the checklist (i) interpolating a value based on the observed condition and two possible conditions listed in the checklist and (ii) assigning the interpolated value as the score for the item;

(d) calculating a supply side system rating based on the selected values for the supply side;

(e) calculating a demand side system rating based on the selected values for the demand side;

(f) calculating an estimated total efficiency rating for the compressed air system based on the average of the supply and demand side system ratings; and

(g) outputting the estimated total efficiency rating.