Whereas much is known about how humans categorize and reason based on absolute quantities, research investigating the processing of relative quantities, such as proportions, is comparatively limited. The current study used a Stroop-like paradigm to examine adults’ automatic processing of nonsymbolic proportions and how presentation formats modulate this processing. Participants were asked to compare individual components across proportions in six different presentation formats. Congruity between component size and overall proportion affected accuracy of comparison, such that participants were less accurate when proportion (the irrelevant dimension) was incongruent with absolute quantity (the relevant) dimension. Moreover, the congruity effect was modulated by the presentation format. These findings serve as evidence that humans automatically access relative quantity when presented in nonsymbolic formats and provide evidence that the strength of this processing is modulated by the format of presentation.