Approximating the station as a hollow shell of constant thickness, the mass would scale with the surface area. The volume would scale proportional to the surfac

Approximating the station as a hollow shell of constant thickness, the mass would scale with the surface area. The volume would scale proportional to the surface area to the power of 3/2. So 6.6x the mass gets you 6.6x the surface area, which gets you about 17x the volume, or ~5600m^3