You can try JCR. "Journal Citation Reports offers a systematic, objective means to critically evaluate the world's leading journals, with quantifiable, statistical information based on citation data. " : http://thomsonreuters.com/products_services/science/science_products/a-z/journal_citation_reports/
Normally, journals display their Impact Factor and CiteScore on their About Page. However, you have to be careful because predatory journals post fake Impact Factors too. Therefore, a best place to check is on SCImagojr and Thomson Reuters as suggested by previously. You can also try using SCOPUS.
scimagojr.com and webofknowledge.com gives different Q values for the same journal. In earth science for example, "Tectonophysics" is Q1 in scimagojr.com, but Q2 in webofknowledge.com. Similarly, scimagojr.com gives generally one degree higher rank for the same journal. I think webofknowledge is more accurate. If "Tectonophysics" is Q1, then, which Q value will be given to "Nature"?
In a case that you need a MS Excel file with Journal Impact factors for 2019, it is available at: https://www.sciencesoft.cn/wp-content/uploads/2019/06/Journal-Impact-factor_2019.xlsx
As colleague Jakub Fedorčák mentioned ^^ InCites Journal Citation Reports is very handy, especially in a form of MS Excel file. Here is one available at:
After looking at their impact factor, review period, and cost of publication you will select a specific journal for your article. Then you can verify the journal impact factor and its indexes using the following links;
If any journal is indexed on the “Science Citation Index Expanded.” It means journals are included in the core collection of the Web of science, and it is also included in the JCR list. All journals which are included in the core collection of the Web of science have an impact factor. It also has a link to view the journal's profile page, and you will find the journal's ranking and other details.
There is another term used that is known as the “Science Citation Index Emerging.” It means that the journal has been included in the master list of the Web of Science, and its progress is being checked, and sooner or later, it would be included in the core collection list. Several journals, but not all, which are included in the Science Citation Index Emerging list, have impact factors.
Scopus is Elsevier’s abstract and citation database, and it under the control of the Elsevier company. Scopus gives four types of quality measures for each journal: h-Index, CiteScore, SJR (SCImago Journal Rank), and SNIP (Source Normalized Impact per Paper). Scopus awards the impact factor. You can check the impact factor and other details of the journal from the following website.
https://www.scimagojr.com/
Please be clear that the indexation of a journal on the Web of science and impact factors are two separate things.