Network bandwidth is not normally a significant factor to consider for cluster sizing. However, clients require network bandwidth to access information in the cluster. Nodes also need network bandwidth to exchange information (node to node).
In general you can calculate your network bandwidth requirements using this formula:
Bandwidth = (operations per second * item size) + overhead for rebalancing
And you can calculate the
second with this formula:
Operations per second = Application reads + (Application writes * Replica copies)