In an example network flow analysis, sample packets can be received from a stream of packets over a time interval from a network element. The sample packets can be aggregated into a subclass of packets. A sample pool size of the stream of packets in the time interval, a number of sample packets received over the time interval, and a number of sample packets aggregated into the subclass of packets can be determined. An effective sampling ratio (ESR) from the sample pool size of the stream of packets in the time interval and the number of sample packets received over the time interval can be calculated. An extrapolated flow for the subclass of sample packets can be calculated by multiplying the ESR by the number of sample packets aggregated into the subclass of packets.