This dataset contains allometry measurements on corals in tanks conditioned to simulate varied carbon dioxide partial pressure to test how coral colony size modulates PCO2 and temperature sensitivity in a branching acroporid. Data for Figure 1 in a manuscript submitted by P. Edmunds and S. Burgess to J of Experimental Biology in 2020 titled 'Emergent properties of branching morphologies modulate the sensitivity of coral calcification to high PCO2' This material is based upon work supported by the U.S. National Science Foundation under Grant No. OCE 16-37396 (and earlier awards) as well as a generous gift from the Gordon and Betty Moore Foundation. Research was completed under permits issued by the French Polynesian Government (Délégation à la Recherche) and the Haut-commissariat de la République en Polynésie Francaise (DTRT) (Protocole d'Accueil 2005-2020). This work represents a contribution of the Moorea Coral Reef (MCR) LTER Site.