The surface roughness Rq is used for the calculation of the specific lubricant film thickness Λ. It is a root mean square roughness Rq or RRMS. According to (Niemann, et al., 2005), an approximation is given as Rq ≈ 1.25∙Ra.
According to (Baalmann, 1994), an estimate for a usual composite roughness is given by . This formula according Baalmann is used when the sizing button next to the input field is clicked.