Abstract The currently small size computers use and the high tendency to use human – voice interfaces to interact with any systems lead to merge these technologies. But implements strong Speech To Text algorithms on a small micro controlled system will reduce its computational capacity getting lower the system performance to execute other tasks. This work presents some selection criteria and a methodology to evaluate the Speech To Text services, using similarity and speed as metrics and the results obtained from an experiment deployed on a Raspberry Pi 3 using the proposed methodology with Spanish speakers. The application of the proposed methodology helped to detect the Google’s STT system as a best option over IBM and Microsoft STT systems because shows a faster conversion and better similarity measures.