This paper describes a simplified procedure to obtain the uncertainties when converting a set of network parameters to another form. The method is based on a general matrix transformation technique. The technique relies on a transformation matrix that describes the relation between two network parameter definitions and two matrix equations. This paper extends the technique with two new matrix equations to also transform the uncertainties in the network parameters by relying on the same transformation matrix. The proposed method is exemplified by the conversion of S-parameter measurements with uncertainty (of a 30-dB attenuator) to G21 with uncertainty. The proposed method for uncertainty conversion is also compared with an analytic expression for S-parameter to G21 conversion.