Abstract: Background and Objective: The guaranteed and controlled load services’ provisioning of, the present Internet operates on the principle of admission control, in which a flow is set-up that conforms to IETF’s (Internet Engineering Task Force’s) T-SPEC or traffic specification. A parameter of this specification is the flow’s sustainable rate. Similarly, the Committed Information Rate (CIR) is one of the parameters defined by Carrier Ethernet or Transport Ethernet services’ providers in their Bandwidth Profiles, for billing for bandwidth usage and engineering network resources. Presently, no practically known method(s) or formula(s) for determining a flow’s sustainable rate or CIR exists. This study describes the derivation of one such formula. Methodology: An empirical, practically utilizable formula for calculating the average rate of any data communications’ traffic flow was derived and a numerical example to illustrate the application of the formula was given. Results: Numerically obtained values showed that, for the same maximum delay, the longer the distance between the source and destination of a flow, the higher the average rate that should be specified for the flow; the higher the maximum delay, the smaller the average rate that should be specified: Both are physically realistic situations. Conclusion: The formula is quite simple for practical applications. With it, Applications can communicate average rates’ values that should be provisioned for, by nodes on the paths of the flows to the different destinations.