Railing Materials Calculator

Already ran the Deck calculator's railing run? Use Active project. Otherwise enter your own measurement manually.

Chained railing run

Enter a railing run on the deck calculator first to prefill this run.

Railing runftTotal length of railing to build.Max post spacingoptionalft6 ft on-center is a practical reference default for wood 4x4 posts, not an IRC-mandated number.Corner countoptionalHow many corners the railing turns. Enter 0 for one straight continuous run and the posts are counted exactly. A run length on its own cannot say — a straight railing and an L-shaped one of the same length need different numbers of posts — so this is asked for rather than assumed.Baluster widthoptionalinWidth of a single baluster/spindle. Needed to solve the spacing: 3/4 in square stock and a 2 in turned spindle differ by about a fifth in the count, so it is not assumed.Max openingoptionalinLargest allowed gap between balusters. Defaults to 4 in, the standard IRC guardrail rule that a 4 in sphere must not pass through.

Enter a railing run to size posts, rails, and balusters.

You'll need

Railing material estimate

Warnings

INFO No railing run is saved in the active project yet, so the manual run is being used.
ERROR Enter a railing run greater than zero.
INFO 6 ft on-center is a practical reference default for wood 4x4 posts, not an IRC-mandated number -- verify against your post size, material, and local code.

Detail values

Railing run used: — ft
Post spacing: corner count not entered

Assumptions

Max post spacing: 6 ft on-center (6 ft is a practical wood-4x4 reference, not an IRC-mandated figure)
Railing shape: corner count not entered -- posts not counted
Max baluster opening: 4 in (IRC R312.1.3: a guard passes no 4 in sphere)

Included: top rail, bottom rail.

Not included: labor, delivery, permits, disposal of waste material.

Formula details

Bay count: ceil(railingRun / maxPostSpacing)
Post count: bayCount + 1
End posts included. Exact for one straight continuous run, which is why the corner count is asked for: a railing that turns needs a post at each corner, and the sections either side of it are re-divided around that fixed post.
Post spacing: railingRun / bayCount
Evenly distributed so no bay exceeds the max spacing.
Top/bottom rail length: railingRun
Baluster count and gap: count = ceil(runInches / (balusterWidth + maxOpening)); gap = (runInches / count) - balusterWidth
Solved so no opening exceeds 4 in across the whole run. IRC R312.1.3: a guard has no opening, from the walking surface to the required guard height, that passes a 4 in diameter sphere. The section's stair-triangle and open-stair-side exceptions are not modelled here.

Material List

About this calculator

Pull the railing run and baluster count from the deck calculator's baluster spacing section, or override manually.

FAQ

Can I use this without the deck calculator?

Yes. Switch to manual and enter the railing run directly.

Where does the 6 ft post spacing default come from?

It's a practical reference default for wood 4x4 posts, commonly cited across deck-building trade guides -- the IRC itself requires the guardrail assembly to resist a 200 lb load rather than specifying a fixed spacing number, so this is editable and should be verified against your post size, material, and local code.

Does this include balusters?

If a baluster count is available from the deck calculator's baluster spacing section, it's passed through here as a line item alongside posts and rails.