On Mon, 9 Jun 2014 12:20:11 -0700 (PDT), wrote:

On Sunday, August 15, 2004 1:58:21 PM UTC-4, Bill Rogers wrote:
On Sun, 15 Aug 2004 09:54:29 -0400, "J. Clarke" wrote: Why? The support posts are vertical and each the same height, and those the same height as the ones holding the horizontal deck railing. Since there is at least one post at the top and at the bottom, the rail must wind up parallel [same angle] to the stairs. Read the thread title. The OP did not ask whether she needed to know the angle, she asked how to find out what it was.Read the reply. It's better to give stronger advice than to answer a questionable question. She can find the angle by trig as well, but I wouldn't advise that either. The point is that there is no need to measure the angle, and it does little good. A better way is simply a better way. Any angle [stair to post] can be copied using an adjustable bevel if necessary.Bill.

Agreed. Make it the same height at the top and the bottom. It will naturally align. The angle is unnecessary to know.
It is necessary to know if the OP is building a railing off-site -
like a wrought iron railing that is welded together at the right angle
and installed in one piece.
Easy enough to canculate anyway if you know the run and the rize.