Background and aim: Citation is the most important scientific elements and assessment index among researchers, universities and research centers. The aim of this study was to compare the citations of researchers in the field of engineering in Scopus, Google Scholar and Google Books.

Material and methods: This study investigated the relationship between citations using citation analysis and data were extracted from Scopus from 2008 to 2012. Totally, 100 subjects were randomly selected using Webometric Analyst, and the numbers of citations were transferred to SPSS and analyzed.

Findings: Results showed that the median of citations to articles was 4, 6 and 1 in Scopus, Google Scholar and Google Books. Although there was no difference between the mean of Google Scholar and Scopus, it was found that the citations had high distribution based on variance values. Most of the citations to articles in Google Scholar, Scopus and Google Books were 1061, 652 and 72, respectively.

Conclusion: There was a direct and significant relationship between the citations of Scopus and Google Scholar; therefore, the use of all three bases regardless of overlapping articles showed the better results in evaluation of scientific outputs. Moreover, even, assessing the scientific outputs can be performed through Google Scholar in case of lack of access to Scopus.