IT Cost as a Percentage of Revenue is one of the most common measures of the efficiency of IT operations.
Total spend on IT (comprising hardware, software and networking costs - including outsourcing costs) as a percentage of annual revenues (sales).
This indicator will be included in my book: Key Performance Indicators - the 100 measures every manager needs to know, which contains an in-depth description of this KPI, as well as practical advice on data collection, calculations, target setting, and actual usage.