We consider dimensioning of data networks. The network is modeled in a dynamic setting where elastic flows (file transfers) arrive randomly and share the bandwidth according to balanced fairness. Simple methods are derived for determining the link capacities so that given flow-level throughput requirements are satisfied. We consider two different approaches to define the throughput requirements: single constraint on average throughput in the network and separate constraint for every route. The results enable a simple characterization of the order-of- magnitude of the required capacities, which can be utilized in practical network planning and dimensioning.