In general, techniques are described for allocating virtual output queue (VOQ) buffer space to ingress forwarding units of a network device based on drain rates at which network packets are forwarded from VOQs of the ingress forwarding units. For example, a network device includes multiple ingress forwarding units that each forward network packets to an output queue of an egress forwarding unit. Ingress forwarding units each include a VOQ that corresponds to the output queue. The drain rate at any particular ingress forwarding unit corresponds to its share of bandwidth to the output queue, as determined by the egress forwarding unit. Each ingress forwarding unit configures its VOQ buffer size in proportion to its respective drain rate in order to provide an expected delay bandwidth buffering for the output queue of the egress forwarding unit.