Characteristics of a multiwire transmission line with inhomogeneous medium, as used for wiring in digital equipment, are investigated with respect to the cross-coupling noise, or cral. Formulas of crosstalk magnitudes are derived. Then they are simplifled for two specific kinds of transmission lines, i. e., a kind of strip lines and a line with equalized coupling. They are ready for straight-forward calculation by a computer, and agree with experimental results very well. A special kind of norm is introduced to simplify matrix calculations into scalar approximations to estimate a guaranteed upper bound of crosstalk voltages in the general case. It is found useful as a criterion in the first step of design considerations.