Feb
There are at least three ways to arrange the balusters on your stairway. The most popular, I think, is where the baluster bases are oriented horizontally and the tops follow the “rake” angle of the handrail.

Angled top-horizontal bottom
By the way the rake angle is the angle of the rise of the stairs. Below is a graphic describing it.

Rake angle
Another method for arranging the balusters is when both the baluster bases and the tops of the balusters follow the “rake” angle of the stairway.

angled top angled bottom
And lastly balusters can be attached to a knee wall that rises above the tread. In the first two examples, the balusters are attached to the treads but here they are attached to a small wall. These balusters are all the same length. This arrangement is called a “closed stringer”.

knee wall arrangement
It should be said here that some stairways have two balusters per tread and some have three. In most communities there is a four inch rule for baluster spacing. The four inch rule means that balusters may not be spaced farther than four inches. The restriction is to prevent a child’s head from being caught between the balusters.

four inch rule
So whether you can get away with two balusters will depend on the depth of your treads and the size of your balusters. A larger baluster or shallow tread means you may be able to accommodate the four inch rule with two balusters per tread. Smaller balusters or deeper treads will mean that three balusters are necessary.
[...] to achieve a baluster arrangement that has the bases and the tops following the rake angel. See my baluster arrangement [...]