Baluster Spacing Calculator

An even on-center layout, with gaps checked against the 4 inch sphere rule.

Project Details
Enter your measurements and requirements
$
Results
Calculated estimates for your project
Balusters17
On-center spacing5 3/8 in (5.417 in)
Gap between balusters3 7/8 in (3.917 in)
First center from post4 5/8 in
Gap checked againstUnder 4 in: IRC 2021 R312.1.3, not yet reviewed by a licensed professional
Estimated cost$68

Turn these numbers into a build plan.

  • 17 balusters
  • 5 3/8 in on center
  • 3 7/8 in gap
Materials List
Recommended materials and quantities
Balusters17

Mark centers at: 4 5/8 in, 10 1/16 in, 15 1/2 in, 20 7/8 in, 26 5/16 in, 31 3/4 in, 37 1/8 in, 42 9/16 in, 48 in, 53 3/8 in, 58 13/16 in, 64 1/4 in, 69 5/8 in, 75 1/16 in, 80 1/2 in, 85 7/8 in, 91 5/16 in

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Project plan · built from your numbers

Install 17 balusters

17 balusters on a 96 in rail, 5 3/8 in on center, leaving 3 7/8 in gaps.

Materials
$68
Time
1 day
Level
Easy
5 steps 4 tools 2 materials
  1. 1

    Check rail length

    Measure between posts at the rail, in case the posts lean.

  2. 2

    Cut a spacer

    Cut a block to 3 7/8 in to keep every gap the same.

  3. 3

    Mark the centers

    Mark the first center at 4 5/8 in, then every 5 3/8 in.

01 · Your numbers
Balusters
17
On center
5 3/8 in
Gap
3 7/8 in
Est. cost
$68
02 · The plan

5 steps · 4 tools · 2 materials

2 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

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Install 17 balusters

Finished in 1 day · $68 DIY

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How to space balusters

A 4 in sphere must not pass through a guard, checked here against IRC 2021 R312.1.3, which no licensed reviewer has signed off for this site. Confirm with your inspector. See the deck building and stair building guides.

  1. Measure between posts. Measure at the rail, in inches.
  2. Find the count. Add balusters until the gap drops under the limit.
  3. Work out the gap. Gap = (rail - balusters x width) / (balusters + 1).
  4. Mark centers. The first center is one gap plus half a baluster from the post.

Frequently asked questions

How do you calculate baluster spacing?

Subtract the total baluster width from the rail length and divide by the number of gaps, which is one more than the balusters.

How many balusters for an 8 ft section?

With 1.5 in balusters, a 96 in span takes 17, leaving gaps just under 4 in.

Is the limit different on stairs?

The 2021 IRC allows a 4-3/8 in sphere on the open side of stairs. Local codes vary, so ask your building department.

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