The minimum in-stent lumen diameter is a predictor of restenosis. Stent dimensions provided by manufacturers are derived from in vitro tests. The aim of this study was to compare actual stent dimensions obtained by angiography and intracoronary ultrasound with dimensions that would be expected theoretically for a given inflation pressure in a cohort of 100 non-complex lesions suitable for direct stenting. Significant differences were found between the theoretical diameters and those observed by angiography and ultrasound. The actual-to-theoretical diameter ratio was 0.83 (0.09) when measured using angiography and 0.78 (0.10), using intravascular ultrasound. In lesions without severe calcification, stent dimensions were significantly smaller than indicated by the manufacturer. Nominal figures should not be used as reference values for stent implantation.