Use InCites Journal Citation Reports to find the impact factor of a journal. In Web of Science, click on Journal Citation Reports in the upper menu bar.
To see information about one journal at a time
On the left side, find Go To Journal Profile. Type the full name of a journal in the Master Search box. See the impact factor, 5-year impact factor, total cites, etc. See how the journal's rank has changed over time.
To compare journals in a subject category
Find Select Categories on the left, choose a category and close the pop-up window, and click on submit in the bottom left column. It will show a list of the journals in that category ranked by impact factor.