The choice of preferred access route for transcatheter aortic valve implantation (TAVI) is mainly guided by the minimal aorto-femoral tract diameter. Currently, projection angiography (XA) and CT-angiography (CTA) are used interchangeably to assess this diameter in the TAVI work-up. We aimed to assess the agreement of XA and CTA diameter measurements in TAVI candidates. Diameters of 700 aorta-iliac segments of 102 TAVI candidates were analyzed on both XA and CTA. The diameters on XA were measured manually, for the CTA-based analysis semi-automated segmentation software was used. Paired sample T test was used to evaluate differences in diameter measurements between the modalities. Disagreement on the suitability for a transfemoral (TF)-TAVI approach was identified. The interobserver agreement for both measurements was assessed by calculating the intraclass correlation coefficient (ICC). The average diameters were 10.1 ± 1.8 mm and 8.4 ± 1.7 for XA and CTA respectively. The mean paired difference was 1.73 mm (p < 0.001). For 18 patients (17.6 %) diameters measured on CTA images, were bilaterally less than 6 mm, whilst XA indicated a minimum diameter exceeding 6 mm. For both modalities, the interobserver agreement was excellent (ICC 0.95). Diameters measured semi-automatically on CTA were statistically significantly smaller compared to XA. This should be acknowledged in the work-up for selecting the most appropriate approach for TAVI. In our population 17.6 % of patients would have been denied a transfemoral TAVI based on CTA measurements, whilst XA suggested diameters sufficient for a TF approach.