Differences in size, mean number of references per paper in journals, ageing of information and disciplinarity of some subfields in chemistry were studied in order to explain different average impact factors for journals. A new indicator —Standard Journal Impact — is suggested, which may be used as a standardized (i.e. comparable) impact indicator for journals in different subfields. The main reason for the lower impact factor for journals of the macromolecular chemistry subfield may be the lower extent of the application of their results by other subfields.