In structured peer-to-peer (P2P) networks participating peers can join or leave the system at arbitrary times, a process which is known as churn. Many recent studies revealed that churn is one of the main problems faced by any Distributed Hash Table (DHT). In this paper we discuss different possibilities of how to estimate the current churn rate in the system. In particular, we show how to obtain a robust estimate which is independent of the implementation details of the DHT. We also investigate the trade-offs between accuracy, overhead, and responsiveness to changes.