This study focuses on the conceptual category of mirativity and its constructional construal in English. We propose an operationalization of mirativity with a view to investigating the phenomenon within the usage-based quantitative methodology of multifactorial analysis (Geeraerts, Grondelaers, & Bakema, 1994; Gries, 2003). The proposed operationalization is founded on two usage dimensions, i.e., the degree of performativity of the utterance and the degree of incongruity of the described event. It is argued that mirativity, in its prototypical form, can be operationally defined as a combination of high levels of these two variables. The feasibility of this operationalization in usage-based quantitative research is tested in a case study investigating three surprise-encoding constructions in English: [what + the + np], [what + a + np] and [to + my + np]. The data, amounting to 350 observations of the three constructions, were extracted from dialogic online diaries and submitted to detailed manual annotation and subsequent multivariate statistical modeling. The results reveal a usage continuum ranging from [what + the + np] through [to + my + np] to [what + a + np] relative to the high degrees of performativity and incongruity.