Ratio of the average disc outer radius r_out to the BBH separation D₁₂ as a function of the BBH mass ratio q. The colored points correspond to various BBH separations. For any given BBH mass ratio, the values of r_out/D₁₂ are very close for all separations showing that this ratio does only depend on the BBH mass ratio, q. We can also notice that all values of r_out are smaller than both the size of the Roche lobe (Eggleton 1983) and the location of the innermost Lindblad resonance as expected for any stable accretion disc.