In the absence of well-documented pumping tests, we investigate whether a reliable estimate of transmissivity T can be obtained using historical records of specific capacity data in granular and fractured-rock aquifers. Transmissivity values are calculated from the specific capacity data Q/s in several hundred wells located in the Saguenay-Lac-Saint-Jean region (Canada), with an iterative method applied to the Cooper-Jacob equation. The results are compared with short- and long-duration pumping tests performed throughout the region. We demonstrate that values of transmissivity compare well between the different types of tests for each lithology, when the scale of the test is similar. Therefore, using historical information easily increases the number of transmissivity values that can be estimated over a region. These values can be integrated in regional numerical models. Moreover, this study shows that T = 4.48(Q/s)^1.15 with R² = 0.66 for granular aquifers. This new empirical relationship can be used in similar environments.