Stemming from centrally planned church architecture, the domestic rotunda type counts as one of the most renowned examples of Renaissance architectural conception. Often considered a physical and earthly manifestation of the divine, architects ordained rotunda symbolism through architectural ratio and proportion. While mostly linked to Italian examples, the rotunda typology also affected British architecture, as derived from the models of Serlio and Palladio. By combining 3D scanning and CAD analyses with historical methods, we scrutinise how commonplace architectural ratios shaped British rotunda plans in the cases of Hopetoun House and Chiswick House. At the same time, the architectural ratio proved a flexible tool to imitate and emulate Italian architectural models in its British context, making evident the richness and versatility of architectural models that British architects collated.