To propose a standardization of calculus of the ankle-arm index as a diagnostic tool in the clinical setting and epidemiology of peripheral arterial disease, we aimed to study the reproducibility of its measurement through 15 different modes of calculation. The study was performed in a group of 194 vascular laboratory outpatients of a tertiary center. The intra- and interobserver variability was assessed by the intraclass correlation coefficient of agreement and the Bland & Altman method. Methods where the numerator was calculated by the average of posterior tibial and dorsalis pedis artery systolic pressures revealed to be the best reproducible. According to this study and former researches on this topic, we recommend the use of the average of posterior tibial and dorsalis pedis artery systolic pressures of the weakest limb for the numerator and the average of systolic pressures of humeral arteries for the denominator of the ankle-arm index.