Despite the considerable expansion in the number and extent of marine protected areas during the past century, coverage remains limited amid concerns that many marine protected areas are failing to meet their objectives. New estimates of global marine protected area, based on the database maintained by Sea Around Us, revealed a degree of progress towards protecting at least 10% of the global ocean by 2020. It is estimated that > 6,000 marine protected areas, covering c. 3.27% (12 million km2) of the oceans, had been designated by the end of 2013. However, protection is generally weak, with c. one-sixth (1.9 million km2) of the combined area designated as no-take areas (i.e. fishing and other extractive activities are prohibited). Additional large tracts of ocean will need to be protected to reach the 10% target, and we investigate hypothetical scenarios for such expansion. Such scenarios offer a one-dimensional measure of progress as they do not address aspects of other global targets, such as Aichi Target 11, which will help to ensure that marine protected areas meet their objectives and achieve conservation outcomes.