I forgot to say anything about design and layout.
Let's say that the length of the wall is eight feet.
Let's say that the height of the wainscot is 36" (I've always thought
that a wainscot looked best if it was a bit more than one third of the
height of the wall).
Let's say that you have a 1" cap and a 3/4" apron.
Let's say that you expose 2" of the top rail (which will actually be
2" plus the 3/4" that the apron will lay on, or 2-3/4") and 2-1/4" of
the bottom rail ( which will actually be 2-1/4" plus the 4-1/2" of the
baseboard, remembering the 1/2" that we are leaving above the floor,
for a total width of 6-3/4").
Lets say that you have a baseboard assembly that is 5" high (including
the shoe, and allowing for the half inch gap at the floor).
You will wind up with a panel ( or what looks like a panel) that is
Most folks like the Golden Rectangle, which is a simplified ratio of
about 1 to 1.6.
I prefer that the vertical is the 1.6 part, so the ideal panel would
be the given of 25" high by the theoretical 15-5/8" wide.
If your stiles are 2", the greatest number of 15-5/8" panels that you
can fit on an eight foot wall is 5.
If you make your panels 15-5/8", this will give you 78-1/8" of panels.
96" of wall length, minus 78-1/8" of panels, will leave you 17-7/8" of
stiles, which will be split equally into six pieces - for a stile
width of almost 3" - No good.
Do the math the other way, keeping your stiles at 2", and you will get
12" total width of stiles, leaving 84" of total panel width, divided
into five panels, giving you a unit panel width of 16-51/64".
Although it is not perfect, it should give you the best approximation
of the look that you want.
I've always preferred to adjust the panel width and keep the stile
width the same throughout the room, as I think it gives more rhythm to
Tom Watson - WoodDorker