Google Scholar also provides citation information. The cited numbers may be duplicates of what is provided in Web of Science. Google Scholar also includes some book chapters, conference proceedings, and other documents which aren't included in Web of Science.
(Google Scholar sometimes duplicates citations leading to inaccurate numbers. It is still a good way to find similar articles and to get a general idea of citation numbers, especially for items not in Web of Science.)
Using the Google Scholar advanced search form, and searching for the same article provides this:
The cited by numbers are the same as in Web of Science. Usually, the cited numbers from Web of Science and Google Scholar are different.