Deck Railing Calculator
Railing is sold in linear feet but built from posts, rails and balusters. Enter your deck size and open sides to get all three counts at once.
Result
- Railing run44lin ft
- Posts (6 ft max on center)9posts
- Balusters96balusters
- Top + bottom rail88lin ft
- 8 ft rail boards11boards
- Railing height36 in(3 ft)
How it works
rail run from selected sides; posts = run ÷ 6 ft + 1; balusters = run×12 ÷ (gap + 1.5 in)
- Perimeter = 2 × (16 + 12) = 56 ft
- Railing run for 3 sides = 44 ft
- Posts = ceil(44 ÷ 6) + 1 = 9 (6 ft max spacing typical)
- Baluster pitch = 4" gap + 1.5" baluster = 5.5"
- Balusters = ceil(528 ÷ 5.5) = 96
- Rails (top + bottom) = 88 lin ft → 11 boards at 8 ft
How the deck railing calculator works
Start with the run: the total linear feet of deck edge that needs a guard. A typical deck open on the house side subtracts that wall from the perimeter.
Posts carry everything, spaced up to about 6 feet apart in common code — closer if your railing system specifies it. Corners always get a post.
Balusters fill between top and bottom rails. Most codes cap the gap at 4 inches (a 4" sphere can't pass through), so a 1.5" baluster sits on a 5.5" pitch.
Formula
posts = run ÷ 6 ft + 1; balusters = run × 12 ÷ (max gap + 1.5 in)
Worked example: 3 sides of a 12 × 16 ft deck
- Perimeter = 2 × (16 + 12) = 56 ft
- Three sides (ledger open) = 56 − 12 = 44 ft of railing
- Posts at 6 ft max on center = ceil(44 ÷ 6) + 1 = 9 posts
- Baluster pitch = 4" gap + 1.5" baluster = 5.5"
- Balusters = ceil(528 ÷ 5.5) = 96 balusters
- Rails (top + bottom) = 88 lin ft → 11 boards at 8 ft
Railing materials per 10 ft of run
| Component | Per 10 ft | 44 ft run | Notes |
|---|---|---|---|
| Posts | ~3 | ~9 | 6 ft max on center typical |
| Balusters (4" gap) | ~22 | ~96 | 1.5" baluster + 4" opening |
| Top + bottom rail | 20 lin ft | 88 lin ft | 2 rails per run |
| 8 ft rail boards | 3 | 11 | For a 2-board rail profile |
Common residential practice. Baluster gaps and guard heights are regulated by local code.
Frequently asked questions
How much railing do I need for a 12×16 deck?
About 44 linear feet for three sides (56 ft perimeter minus the 12 ft house side), or the full 56 ft if all four sides are open. That's 9 posts, roughly 96 balusters at a 4" gap, and 88 linear feet of rail.
How far apart should railing posts be?
6 feet on center is the common maximum for residential decks, with a post at every corner. Some railing systems require 4–5 ft; follow the manufacturer's specification over the general rule.
What's the maximum gap between balusters?
4 inches in most jurisdictions — the standard is that a 4-inch sphere cannot pass through any opening in a guard. Measure the clear gap, not the center-to-center spacing.
When is a deck railing required?
Guards are typically required wherever the walking surface is more than 30 inches above grade. Heights are usually 36" for residential decks and 42" in commercial settings — confirm with your local code before building.