Needle and syringe program (NSP) coverage is commonly used to assess NSP effectiveness. However, existing measures don't capture whether persons who inject drugs (PWIDs) stockpile syringes, an important and novel aspect of NSP coverage. In this study, we determine the extent of stockpiling in a sample of Australian PWIDs and assess whether including stockpiling enhances NSP coverage measures. As part of the Illicit Drug Reporting System study, PWIDs reported syringes procured and given away, total injections in the last month, and syringes currently stockpiled in 2014. We calculated NSP coverage with and without stockpiling to determine proportional change in adequate NSP coverage. We conducted receiver operating characteristic curve analysis to determine whether inclusion of stockpiled syringes in the measure improved sensitivity in discriminating cases and noncases of risky behaviors. Three-quarters of the sample reported syringe stockpiling, and stockpiling was positively associated with nonindigenous background, stable accommodation, no prison history, longer injecting careers, and more frequent injecting. Compared with previous measures, our measure was significantly better at discriminating cases of risky behaviors. Our results could inform NSP policy to loosen restricted-exchange practice, allowing PWIDs greater flexibility in syringe procurement practices, promoting greater NSP coverage, and reducing PWIDs' engagement in risky behaviors.