Space balusters so a 4-inch sphere cannot pass. Enter your rail length and baluster width to get the count and exact gap.
Building codes require that a 4-inch sphere cannot pass between balusters, to protect small children. This calculator finds the smallest number of evenly spaced balusters that keeps every clear gap under 4 inches for your rail length and baluster width.
Codes require that a 4-inch sphere cannot pass through the gap between balusters, anywhere on a guard or stair rail, to prevent a child from slipping through.
Divide the rail into equal gaps so each clear opening is under 4 inches. For n balusters there are n+1 gaps; the clear gap is the rail length minus the total baluster width, divided by the number of gaps.
Metal balusters are commonly 0.5 to 0.75 inches; wood balusters are often 1.25 inches. Wider balusters need slightly fewer pieces for the same rail.