# Manning formula > [!warning] >NB: this method is outdated. Use Darcy-Weisbach approach where possible. See [[Flow in partially full pipes]]. The Manning formula or Manning's equation is an empirical formula estimating the average velocity of a liquid flowing in a conduit that does not completely enclose the liquid, i.e., open channel flow. Suggest just reading the [wiki article](https://en.wikipedia.org/wiki/Manning_formula) on this one.