Deck Railing Calculator

Railing material follows six steps, and every value in them comes from your project:

1. Select the deck sides that receive railing, or enter your railing runs.
2. Subtract gates and openings.
3. Enter the maximum post spacing specified for the project.
4. Calculate the post bays and posts, run by run.
5. Select the railing infill type.
6. Estimate rails, balusters, panels, cable or glass.

For a rectangular deck, add only the sides that receive railing. Front and back run along the deck length; left and right run along the deck width.

Front + Left + Right = Deck Length + 2 × Deck Width

A 20 ft × 12 ft deck railed on the front and both sides gives 20 + 12 + 12 = 44 ft. Then subtract the gates and openings that apply. No side is assumed to require railing.

For each independent run:

Post Spaces = ceil(Net Run Length ÷ Maximum Post Spacing)

Posts = Post Spaces + 1

Each railing run is calculated on its own, because every run needs a post at both of its ends. Two separate 10 ft runs are not the same layout as one continuous 20 ft run. Two 10 ft runs at a 6 ft maximum give 2 spaces and 3 posts each — six posts in total, not five.

Where two selected sides meet, the corner post is counted once instead of twice. In Multiple Runs mode, runs only share an end post when you mark them as connected.

BuildCalcWorks does not choose the spacing. Use the spacing specified by your railing system, approved project plans, applicable requirements or qualified guidance, then enter it here.

Enter the maximum post spacing specified for your railing system or project. BuildCalcWorks does not choose it and does not check it against any requirement. The 4 ft, 6 ft and 8 ft buttons are convenience values for fast entry only — they are not recommended, approved, structurally adequate or code-compliant spacings.

Baluster quantity depends on the space between posts, the actual baluster width and the clear gap you choose. The calculator works section by section, using each post bay's own length, then sums the sections.

Maximum gap. Maximum-gap mode assumes equal clear spaces including the two edge gaps: Gap = (Infill Length − N × Baluster Width) ÷ (N + 1). The calculator returns the smallest quantity whose resulting gaps stay within the maximum you entered.

Fixed gap. Fixed-gap mode fits balusters at the gap you entered and reports the leftover edge space separately — edge gaps do not automatically match the interior gaps.

Enter the actual baluster width and the planned clear gap. BuildCalcWorks does not select a permissible opening size. Spacing estimate from values you entered. Verify the final layout before installation.

Panel quantity depends on the railing-run length, the panel width, whether panels can be cut and how the post bays are laid out. Use the actual product width.

Panel systems differ: some are made to fit a post bay, others can be cut. Use the actual product width and follow the manufacturer's instructions.

Cable quantity is estimated from the railing length and the number of horizontal cable lines you enter, plus your own allowance for terminations and tensioning.

Cable Length = Net Railing Length × Number of Cable Runs

Cable line quantity and spacing are entered by you. BuildCalcWorks does not determine required cable spacing, tension or hardware.

Panel quantity can follow one panel per post bay, or an approximate panel pitch from the width and gap you enter. With a panel height entered, an approximate glass area is shown as well.

Panel quantity is estimated from the dimensions you enter. Glass thickness, structural specification and required supports are outside this calculator.

Openings reduce the rail and infill length but can add boundary posts. Posts at both sides of an opening is a layout assumption you can switch off if your system handles the opening differently.

When an opening splits a run, enter the railing length on each side of it. Post layout then follows the actual segments instead of an assumed opening position. Gate hardware quantities are not calculated.

You can price posts, rails, balusters, panels, cable, glass, caps, skirts and hardware with your own supplier prices. Railing materials only, using prices you enter. Deck framing, stairs, labor and permits are excluded, and unpriced categories are never counted as free.

The Decking Calculator estimates deck boards, joists, beams, posts, footings and fasteners from the same deck dimensions.

Stair railing length is added as a separate material line only. Stair geometry, stair guards and handrail requirements are outside this calculator. Enter it as an additional length and it stays a separate material line in the result.

How BuildCalcWorks calculations are created →