Weight and length data were obtained from state, regional, and provincial biologists for 241 channel catfish (Ictalurus punctatus) populations, representative of the species geographic range. We randomly selected 60% of the populations to develop a new standard weight (Ws) equation and used the remainder as an independent test set. The regression-line-percentile (RLP) technique was applied to the development data set providing a 75th percentile-based metricWsequation of log10Ws(g) = −5.800 + 3.294 log10total length (TL, mm). The English equivalent is log10Ws(lb) = −3.829 + 3.294 log10TL (in). The remaining 98 populations were used to test both current and newWsequations for length-related changes in relative weight (Wr) values. Regression ofWrvalues on TL by population showed that the current equation produced 15% more slopes that were significant (H0: β = 0) than did the new equation. An analysis of significant slopes produced from the RLP-generated equation showed a ratio of 31 positive to 20 negative slopes. The current equation yielded a ratio of 58 positive to 7 negative slopes. Because of the length-related trends inWrvalues associated with the current equation we recommend that researchers apply the new RLP equation to field data for further testing and validation. The new RLPWsequation is valid for application to channel catfish having a TL of 70 mm or greater, as opposed to a minimum TL of 280 mm recommended for the current equation.