How Much Deck Railing Material Do You Need?

For this calculator's example, a 12 ft run measured between end-post centers uses 3 posts and 26 installed balusters. That assumes two equal bays, 3½ in actual posts, 1½ in actual balusters and a 3⅞ in target maximum gap. With the optional 10% spare allowance, buy 29 balusters. Different post locations or widths change the count.

Enter each straight run from the center of its first post to the center of its last post. A run ends at a corner or an opening. Do not enter the clear opening or a deck perimeter that includes unrailed sides. If your existing posts form unequal bays, plan each opening separately.

Add each straight run separately. Select “Shares the previous run's end post” only when both runs physically use the same post at that corner. The shared post is counted once. For a gate or stair opening, add an independent run with the box unchecked; do not include the opening in the run length. Closed loops and branching junctions are outside this calculator's scope.

The shopping list covers usable posts, balusters and the two horizontal wood rails in each bay. It excludes cap rails, gates, brackets, connectors, post anchors, other fasteners and labor. Rail boards are counted at one board per piece, without reusing offcuts. Posts and balusters are counted individually at the lengths your plan requires. The calculator does not work out how many pieces you can cut from longer stock. Confirm rail connection allowances and final post and baluster lengths from your plan. The calculation does not approve post spacing, attachment, guard height or structural loads.