A Query by Tapping system is a database which contains metadata descriptions of songs. The database can be scanned by tapping the melody line’s rhythm of a song requested on a MIDI keyboard or an e-drum. For the processing of queries the system computes the similarity of the query and the content inside the database by applying a similarity measure. Due to the high number of comparison processes in large databases efficiently computable similarity measures are needed. This paper presents two efficiently computable similarity measures which evaluate rhythmic properties of monophonic melodies represented in an MPEG-7 compliant manner. The usage and effectiveness is presented and evaluated with the real time capable Query by Tapping system BeatBank.