Okay, so, first thought is probably "How much living space do you need?" which is a normal question.
I, on the other hand, am about to comment about paper. In particular, my notebooks.
Six millimeters is the amount of space I need between my lines, and the amount of space I need between my lines is six millimeters.
Not five, as in most grids.
Not seven, as in many lined journals.
Six.
And the number shall be six, in the appropriate unit of millimeter.
Also, if you're normal and wondering WTF, Kitt?, I just came across this post about how much space people want in their lined journals, and had an opinion. I know, I know, you're like, "You? Opinion?" and I'm all, "Yes!"