Deck Railing & Baluster Calculator
Find out how many balusters your railing needs and the exact spacing between them — so your gaps stay under the 4-inch building-code limit.
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How to calculate baluster spacing
Building code requires that a 4-inch sphere cannot pass between balusters, so your gaps must be less than 4 inches. Divide your usable railing length by the combined width of one baluster plus the maximum gap to get the baluster count, then distribute the leftover space evenly so every gap is equal and under the limit.
How many balusters per foot?
With standard 1.5-inch balusters and a sub-4-inch gap, you’ll use roughly 2.2–2.4 balusters per foot of railing. Tighter spacing or thinner metal balusters increases the count.
Frequently asked questions
- Why subtract the posts?
- Posts take up part of the run and break the railing into sections, so we remove their width before spacing the balusters.
- What gap should I aim for?
- Target about 3.5 inches. It keeps you safely under the 4-inch code limit even with small build variations.
Plan the rest of your build
- Deck Cost Calculator — total project price.
- Deck Stairs Calculator — risers, treads, stringers.
- Deck Stain Calculator — gallons of stain or sealer.