Green public open spaces (POS) are an important component of healthy, liveable, and sustainable urban environments. Planning policies for POS provision however tend to be evidence-free. A review of Australian state-level POS planning policies and standards was conducted and policy-specific spatial measures generated in GIS. These were linked with health data from the RESIDE survey and relationships examined with weekly walking for recreation and moderate-vigorous physical activity (MVPA). To facilitate the development of a comparable national measure of POS provision, the measures were replicated using a national-level dataset on POS and compared using intra-class correlations. Sixteen POS policy standards relating to the location, amount, access, and size of POS were identified. Only one POS standard was associated with a health outcome: RESIDE participants living in suburbs where 95% of residents lived within 400 m of a park had a three-fold increased odds of doing weekly MVPA. The national dataset did not appear to align with the types of POS typically addressed by urban POS planning policies and showed a low level of reliability with the finer-grain state layer (ICCs 0.185–0.312). These findings support existing literature indicating that neighbourhoods with greater access to POS within 400 m are associated with higher odds of physical activity. The current study suggests that not all POS standards are equal, and more research is required to determine whether current planning standards being implemented are achieving their full potential. The development of national evidence-based, policy-relevant POS indicators has the potential to inform future POS planning policies and decisions.