How to find impact factors
The impact factor of a journal is the average number of times that papers published in that journal have been cited during a specific period. The higher the impact factor the more prestigious the journal is considered to be. The impact factor is computed by dividing the number of citations received in a specific year by the number of articles published in the two preceding years. This number only acquires meaning if it is compared to the impact factors of other journals in the same discipline.
Exact and social sciences
Law Journals: Submissions and Ranking
Apart from the impact factor there are other ways to indicate the reputation/value of an academic journal.
The Eigenfactor is the average number of article citations that are published in articles in a specific journal in the past 5 years. The Eigenfactor takes the importance of the citing journals into account. This indicator can be found on a seperate website and in the Journal Citation Reports.