Hertzsprung-Russell diagram of our final sample, which contains 490 γ Dor stars. The colour-coding gives the Π₀, which is used as an input parameter in the grid modelling. The solid lines indicate the theoretical γ Dor instability strip from Dupret et al. (2005) with a mixing-length parameter α_MLT = 2, while the dashed and dotted lines show the position of the instability strip for α_MLT = 1.5 and α_MLT = 1, respectively.