To date, more than 20,000 patients with severe symptomatic aortic valve stenosis and high-risk or contraindication to conventional surgery have been successfully treated with transcatheter aortic valve implantation (TAVI). The results of the multicentre randomised Placement of aortic transcatheter valve trial (PARTNER) 7 have shown the superior long-term survival of patients who received a transcatheter aortic valve compared to patients who were medically treated. In order to optimise the procedural success rate and minimise the number of complications, patient selection and procedural strategy planning are crucial. Selection of prosthesis size is one of the key steps in this pre-procedural evaluation. Accurate measurement of the aortic valve annulus is pivotal to select the most appropriate prosthesis size and avoid complications such as prosthesis migration, paravalvular aortic regurgitation or aortic annulus rupture. Currently, the reference method to measure the aortic valve annulus dimension is still debated. While 2D echocardiography remains as the imaging modality of first choice to measure the aortic valve annulus, 3D imaging techniques have provided important information on the shape, geometry and spatial relationships of this structure. The present review provides an overview of the different imaging techniques to measure the aortic valve annulus and the inherent clinical implications of each technique.