Microseismic mapping is a valuable tool for assessing hydraulic fracture stimulations. During a stimulation treatment, borehole, near-surface, or surface geophones record passive seismic data. The microseismic events are thought to be shear failures that occur around the opening of a tensile hydraulic fracture as it grows. Over the past several years, there has been a large growth in the number of hydraulic fracture monitoring surveys, along with the number of vendors who acquire and process microseismic data. Here we discuss two attributes of microseismic data which are associated with the size of the passive event: seismic moment and magnitude.