G'day Mark, 6:1 ratio is asthetically pleasing, and when I laid the floor in our last home I used multiples of 6x the board used, ie; 80mm surface x 6 =240mm, 12x=480 18x=720mm etc also made it easier to complete the "L" as thats what we had as well 4.5 metres short side laid across, 9.2 metres laid traditional length ways.