Stair Railing Calculator
Calculate railing length, baluster count, baluster spacing, and materials for stair railings and guardrails.
How It Works
Enter the stair run length (or total run), total rise, and baluster style. The calculator determines: handrail length (following the stair slope), number of balusters needed (based on the 4" sphere rule — no gap wider than 4"), baluster spacing, and a complete materials list including the handrail, balusters, newel posts, brackets, and fasteners. It accounts for the angled installation along the stair slope.
Frequently Asked Questions
What is the 4-inch sphere rule for balusters?
Building code requires that a 4" sphere cannot pass through any opening in the railing. This means the clear space between balusters must be less than 4". With standard 1.25" square balusters, the center-to-center spacing is about 5.25".
How high should a stair handrail be?
IRC 2018 requires stair handrails to be between 34" and 38" measured vertically from the stair nosing. On open sides, a guardrail of at least 36" (residential) is also required. Deck guardrails must be 36-42" depending on local code.
How do I calculate handrail length?
Handrail length = √(total rise² + total run²) + extensions. Code requires the handrail to extend horizontally at least 12" beyond the top riser and one tread depth beyond the bottom riser.
How many balusters per step?
Typically 2 balusters per tread for standard 10-11" treads with 1.25" square balusters. This maintains the 4" sphere rule. For wider treads or thinner balusters, you may need 3 per tread.