Access to parks by urban residents has been associated with higher mental and physical health, social capital, community cohesion, and quality of life. Universal access to safe, inclusive, and accessible green and public spaces in cities and communities has been identified as a Sustainable Development Goal (SDG 11) by the United Nations. To advance and measure progress towards this goal, policymakers require data-driven metrics to quantify access to parks to benchmark their performance and support decisions for resource allocation. However, there are currently no updated, comprehensive and fine-grained datasets on parks that enable large scale comparisons across cities and countries over time. This work leverages globally consistent data on parks from Google Maps, in combination with the computational power of Google Maps Directions API to quantify accessibility to parks across 496 cities in 6 countries. We combined high resolution population data from WorldPop with parks data and navigation estimates to measure: (1) Fraction of the population with access to parks within a 10-minute walk; and (2) the median walking time to the closest park. We find large differences in access to parks between countries, as well as large variability across countries, cities, and commuting zones. To demonstrate how this framework can support cross country comparisons and efforts to track progress towards SDG11, we explore the relationship between access to parks and income in selected countries, finding that the median walking time to a park is shorter for residents of low income neighborhoods both in French and American metro areas.