The literature on whether varying plate size has an effect on consumption is mixed and contradictory. This meta-analysis of 56 studies from 20 papers shows that varying the size of the container holding food (e.g., plate or bowl) has a substantial effect on amount self-served and/or consumed (Cohen’s d = .43). More generally, we found a doubling of plate size increased the amount self-served or amount consumed by 41%. Our analysis resolves the various contradictions of past reviews: we found that the plate-size effect had a substantial effect on amount self-served (d = .51) and on amount consumed when the portion was self-served (d = .70) or manipulated along with (confounded with) plate size (d = 48). However, plate size had no effect on amount consumed when the portion size was held constant (d = .03). Overall, plate size had a stronger effect when participants were unaware that they were participating in a food study (d = .76).