diff --git a/core/net/ip/tcp-socket.c b/core/net/ip/tcp-socket.c
index d697ccdd9..cd26634a1 100644
--- a/core/net/ip/tcp-socket.c
+++ b/core/net/ip/tcp-socket.c
@@ -399,3 +399,9 @@ tcp_socket_max_sendlen(struct tcp_socket *s)
   return s->output_data_maxlen - s->output_data_len;
 }
 /*---------------------------------------------------------------------------*/
+int
+tcp_socket_queuelen(struct tcp_socket *s)
+{
+  return s->output_data_len;
+}
+/*---------------------------------------------------------------------------*/
diff --git a/core/net/ip/tcp-socket.h b/core/net/ip/tcp-socket.h
index 34cb0d6b7..dd7b5c793 100644
--- a/core/net/ip/tcp-socket.h
+++ b/core/net/ip/tcp-socket.h
@@ -284,4 +284,16 @@ int tcp_socket_unregister(struct tcp_socket *s);
  */
 int tcp_socket_max_sendlen(struct tcp_socket *s);
 
+/**
+ * \brief      The number of bytes waiting to be sent
+ * \param s    A pointer to a TCP socket
+ * \return     The number of bytes that have not yet been acknowledged by the receiver.
+ *
+ *             This function queries the TCP socket and returns the
+ *             number of bytes that are currently not yet known to
+ *             have been successfully received by the receiver.
+ *
+ */
+int tcp_socket_queuelen(struct tcp_socket *s);
+
 #endif /* TCP_SOCKET_H */