The propagation constants of dielectric rib waveguides for optoelectronics are calculated by new methods designed either as an advance on typical existing methods, or for comparison with them. The classical variational methods agree with each other, but are somewhat pessimistic in that they underestimate the value of the propagation constant. Vector and scalar finite element or finite difference methods fall into a pattern of agreement with each other. Overall, there is a remarkable consensus between the values and the differences between them which highlights their advantages and disadvantages. The implications for directional couplers are briefly discussed.