Measurement uncertainties are propagated through the matrix calibration of a tristimulus colorimeter. It is shown that reference spectral uncertainties and the colorimeter signal uncertainties during calibration are simply scaled and combined in an applied measurement. Modeling shows that transforming x, y chromaticity and Y luminance can lead to lower chromaticity uncertainties than transforming X, Y, Z tristimulus signals themselves. Accuracy depends on the set of colours used for calibration, especially for measurements of displays. Uncertainties can be large and dominate errors due to accuracy of spectral matching to the CIE colour-matching functions. This is particularly true if commision international de L'Eclariage (CIE) Lab values are to be derived. (c) 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 251-258, 2013