Before data center infrastructure efficiency can be benchmarked using PUE or other metrics, there must be agreement on exactly what power consumptions constitute IT loads, what consumptions constitute physical infrastructure, and what loads should not be counted. Unfortunately, commonly published efficiency data is not computed using a standard methodology, and the same data center will have different efficiency ratings when different methodologies are applied. This paper explains the problem and describes a standardized method for classifying data center loads for efficiency calculations.