Most residential newel posts finish out at 3.5 to 6 inches (90-150mm) square with a post height of 34 to 42 inches (864-1065mm) above the nosing line, but diameter is the wrong place to start. The number that actually determines whether a post passes inspection is load capacity: every guard and its posts must resist a 200-pound concentrated load applied at any point along the top rail, per IRC R301.5 and IBC 1607.9. A 1.5-inch turned baluster held on with two screws fails this test regardless of how it looks. A properly through-bolted 3.5-inch newel usually passes with margin.<\/p>\n\n\n\n
Run the numbers for your own stair with the newel post calculator<\/strong><\/a>, which takes your rail height, post material, and anchoring method and checks the assembly against the 200-lb point-load requirement before you cut anything.<\/p>\n\n\n\n Worked example: a stair with a 108-inch (2743mm) total rise built at 15 risers of 7.2 inches (183mm) actual riser height needs two newels minimum \u2014 a starting newel at the bottom step and a landing newel where the rail terminates at the top. The starting newel’s finished height is measured from the nosing line of the first tread, not the subfloor, and the landing newel is measured from the finished floor of the level surface it sits on. Those two reference lines are not the same plane, so a post cut to one uniform length before installation will read as inconsistent height once both are set.<\/p>\n\n\n\n Newel sizing isn’t one number \u2014 it shifts with where the post sits on the run and what it’s anchored into. Use the table below as a starting point, then verify against your local code edition.<\/p>\n\n\n\nPost Height and Diameter by Stair Configuration<\/h2>\n\n\n\n