The interest in Piano Key weirs (PKW) was increasing over the past years, both in terms of application and hydraulic research. Several systematic model test series were per-formed and published so far, originating from different hydraulic laboratories around the world. Therein, the key geometric parameters dominating the hydraulic capacity of PKWs were identi-fied as developed crest length, transversal weir width, height of the walls and key widths. The present paper compares the available data-sets provided by several laboratories and as con-structed on prototypes, partially including a systematic model testing of the relevant parame-ters. The present overview is based on the geometrical dimensions of the investigated and de-signed PKWs, without giving any hydraulic examination.