Biases in the perceived area of different shapes: A comprehensive account and model.

Common daily tasks require us to estimate surface area. Yet, area judgments are substantially and consistently biased: For example, triangles appear larger than same-area squares and disks. Previous work has explored small subsets of shapes and related biases in area perception to one or two geometric features, such as height or compactness. However, a broader understanding of shape-related biases is lacking. Here, we quantify biases in area perception for a wide variety of shapes and explain them in terms of geometric features. In four online experiments (each N = 35), typical adult observers made two-alternative forced choice judgments ("which stimulus has larger area?") for pairs of stimuli of different shape, orientation, and/or area. We found clear shape-related biases that replicate known biases and extend them to novel shapes. We provide a multipredictor model (R² = .96) that quantitatively predicts biases in perceived area across 22 shape/orientation combinations. (PsycInfo Database Record (c) 2025 APA, all rights reserved).