Humans perceive ratios of spatial and temporal magnitudes, such as length and duration. Previous studies have shown that spatial ratios may be processed by a common ratio processing system. The aim of the current study was to determine whether ratio processing is a domain-general ability and consequently involves common processing of temporal and spatial magnitudes. Two hundred seventy-five participants completed a battery of spatial and temporal ratio estimation and magnitude discrimination tasks online. Structural equation modeling was used to analyze the relationship between ratio processing across domains while controlling for absolute magnitude discrimination ability. The four-factor higher order model, consisting of spatial and temporal magnitude and ratio processing latent variables, showed adequate local and global fit, χ²(44) = 41.41, p = .626, root mean square error of approximation = .000. We found a significant relationship (r = .63) between spatial and temporal ratio processing, suggesting that ratio processing may be a domain-general ability. Additionally, absolute magnitude processing explained a large part (60-66%) of the variance in both spatial and temporal ratio processing factors. Overall, findings suggest that representation of spatial and temporal ratios is highly related and points toward a common ratio processing mechanism across different types of magnitudes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).