Baluster Spacing: How far apart? How many do I need?

This is usually the starting point for those looking to buy spindles or balusters for their deck or porch.  The following is a baluster spacing guide for meeting the 4″ ball rule required by most building codes.  Of course if building codes don’t apply in your situation, you can do what looks best to you.  Space them farther for an airy/sparse look.  Or closer together for a fuller, more robust feel.

1 5/8″ Wood Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles every 4 3/4″ On Center.  The smallest diameter of the turned portion is approx. 7/8″, so with a 4 3/4″ O.C. spacing, you’ll have a 3 7/8″ gap between them at the narrowest portion.  To determine quantity required, take your rail length in inches and divide by 4.75.

2 1/2″ Wood or Polyurethane Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles every 5 1/4″ On Center.  The smallest diameter of the turned portion is approx. 1 3/8″, so with a 5 1/4″ O.C. spacing, you’ll have a 3 7/8″ gap between them at the narrowest portion.  To determine quantity required, take your rail length in inches and divide by 5.25.

3 1/2″ Wood or Polyurethane Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles according to the following On Center spacing:
Revival: 5 1/2″ O.C.
Victorian: 5 3/4″ O.C.
Tuscan: 5 3/4″ O.C.
Rampart: 5 15/16″ O.C.
Classic: 6″ O.C.
Using the above spacing, you’ll have a 3 7/8″ gap between spindles at the narrowest portion.  To determine quantity required, take your rail length in inches and divide by the number above next to your baluster design.

4 1/2″ Polyurethane Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles every 6 1/4″ On Center.  To determine quantity required, take your rail length in inches and divide by 6.25.

5 1/4″ Polyurethane Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles every 6 7/8″ On Center.  To determine quantity required, take your rail length in inches and divide by 6.875.

7 1/2″ Polyurethane Spindle / Turned Baluster

Spacing & Quantity: To meet the 4″ ball rule required by most building codes, space these spindles every 7 3/4″ On Center.  To determine quantity required, take your rail length in inches and divide by 7.75.

Square Balusters, Wood or Composite

For square baluster spacing, simply add 3 7/8″ to the width, and that should be your on-center spacing.  It will leave a 3 7/8″ gap between them:
1 5/8″ wide Wood Baluster: 5 1/2″ on-center
1 3/4″ wide Polyurethane Baluster: 5 5/8″ on-center
2 1/4″ wide Polyurethane Baluster: 6 1/8″ on-center
2 1/2″ wide Wood Baluster: 6 3/8″ on-center
3 1/2″ wide Wood Baluster: 7 3/8″ on-center

So how many spindles or balusters do I need for my railing?

To come up with the quantity, take the length of rail (in inches) and divide by the on-center spacing, and subtract one.  You subtract one because they will be centered in the rail between two posts, columns, etc.  For example, you have a 8′ rail (96 inches) and are using the 3 1/2″ Classic Porch Spindle (our best seller).  96 divided by 6 = 16.  Minus 1 = 15.  So you’ll need 15 spindles for an 8′ section of rail.

Is there a baluster spacing calculator?

We recommend you download a baluster spacing calculator on your smartphone.  There are many.  Just search “baluster spacing” or “baluster spacing calculator” in your regular app store and you should have several options (both paid and free).  These apps will help you keep the exact same spacing between all spindles/balusters regardless of the length of rail section.  And you’ll have it right on the jobsite.

Make a spacer to use as a baluster spacing template or jig.

Baluster Spacing

Here we made a simple spacer out of scrap wood.  The spacer width should be your on-center spacing minus the baluster width.  This picture shows our popular 2 1/2″ turned balusters.  We took the recommended on-center spacing of 5 1/4″ and subtracted the baluster width of 2 1/2″.  5.25 – 2.5 = 2.75.  So we cut a spacer 2 3/4″ wide.  This results in a baluster spacing that meets building codes and is easy to install.  You’ll still want to measure and mark your baluster spaces to double check your spacing isn’t getting off as you move along with the spacer template.

What about stair baluster spacing?

Most stair baluster spacing codes throughout the country have the same 4″ ball rule as your deck rail.  Use the same spacing rules as shown above for your stairs.  In theory, a turned spindle could be spaced a tiny bit farther apart due to the thinner turned portions not lining up with each other.  But that level of nit-picking gives me a headache and might look goofy.  Let’s use the same baluster spacing rules as above and move forward with our project!

Still want help with your baluster spacing or quantity?  No problem.  Call and talk with our professionals about your project.

5 thoughts on “Baluster Spacing: How far apart? How many do I need?”

  1. we are going to have a new railing with 3 inch glass spindles (balusters?) installed. What kind of space should there be between those kind of spindles?
    Thanks so much for you help!!!

    1. Thanks for the question. I’m not sure the exact design of your spindles, but with our 2 1/2″ Turned Porch Spindles, you’ll want to space them every 5″ on center. With the 2 1/2″ Square Balusters, a 6″ on-center spacing will work well. If you send us a picture or diagram of your spindles, we can recommend a spacing.

  2. Thanks for pointing out that most building codes include a 4″ ball rule about banister spacing. My husband and I are interested in having wood railings designed for our porch and deck. The info you shared will help us not violate any codes, so thank you!

  3. Thanks for explaining that most building codes have a 4″ rule about the spacing of railings. My husband and I want to get new wood railings installed for the upper level of our back patio to make it safe for our kids to enjoy. I’m glad I read your article and got a better idea of the applicable building codes we’ll need to follow for the project!

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