Here's the spine of your railing project. Described height is the finish height of the railing. Some local code requires 42in, some 36 in, so check what your local requirements are. You can add a handrail, which tend to add less than an inch in height. Spacing between the post is also based on local code, which tends to be between 4 feet and 8 feet. So, if you're covering a span of 20 feet, and code requires post every 4 feet you would need 6 posts. (20ft / 4ft) + 1=6. Feel free to contact us with any questions. We're here to help make your project happen!