Manuscript Version 3 - accepted by the IEEE Journal of Photovoltaics. The final version is available at https://doi.org/10.1109/JPHOTOV.2023.3242117 Abstract: Bifacial photovoltaic modules are able to convert the solar radiation reaching their front and rear-sides, which means that more electricity can be produced using the same array area as monofacial modules with similar ratings. In some locations, the cost per power unit for such a technology has already become cost-competitive with conventional monofacial modules. The so-called effective irradiance and the bifacial gain are useful metrics, respectively, to assess the solar resource and the performance of bifacial arrays. To calculate the effective irradiance, studies previously published employ rear-side irradiance measurements, whereas to compute the bifacial gain, other works make use of monofacial modules with rating similar to those of the bifacial modules under analysis. In this paper, a straightforward method is presented, allowing to calculate the effective irradiance from the maximum power current, and to calculate the bifacial gain using a power scaling relation. The proposed method was experimentally tested using an outdoor platform with a dual-axis tracking system with bifacial modules. The effective irradiance calculated using the novel method presented nRMSE of 2.88 %, relative to the results obtained using the consolidated method. The bifacial gains obtained were 6.24 % and 6.69 %, respectively, using the proposed and traditional calculation methods. The procedure presented in this study might be useful for the quantification of the effective irradiance and the bifacial gain for PV installations which do not have extensive monitoring hardware.