Two methods have been extended (those due to Tuminello and to Shaw), among the several currently available, for calculating the molecular weight distribution functionW(M)of linear polymers from their rheology data. An extension of Tuminello’s method is proposed by using the terminal Rouse relaxation time as a scaling factor. The 79th percentile of the zero-shear viscosity normalized flow curve is used to evaluate the terminal Rouse relaxation time. Using this technique, it is possible to convert frequency to molecular weight, without the use of an external standard. An extension to Shaw’s numerical technique is also proposed leading to an analytical expression for the polydispersity ratio. For this purpose the Elbirli–Yasuda–Carreau viscosity model is used to describe the flow curve. The development is carried out for both the logarithmic and the power law mixing rules considered by Shaw. Due to the approximate nature of both the original methods that Tuminello and Shaw started out with and the subsequent approximations, the resulting distribution should only serve as a first order approximation to the actualW(M)and the calculated moments ofW(M)may be off by as much as about 50% from their true values. Since the more rigorous inverse problem techniques that are also currently available can offer greater accuracy, justification for the use of the approximate methods discussed in this work rests solely on their relative simplicity and ease of implementation.