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Baluster / Spindle Calculator

Calculate the Perfect Space Between Railing Spindles


Spindles make up vertical guards that support handrails. The guards should be able to support 50 pounds of pressure per square foot.

To determine the correct number of spindles for the guard, measure the length of the railing. Then, count the number of vertical guards and the measure the thickness of each. Next, multiply the number of spindles by the thickness, and then subtract this number from the length of the railing.

Add the thickness of the spindle to the space between each of the guards. Four-inch spacing is standard in many areas. Then, combine the number of spindles with the required spacing.

Divide the rail’s length by the area of the spindle and required spacing to determine the number of spindles. Any partialcalculations should round up to the next whole number.

As a general rule of thumb, it’s a good idea to add an additional 10% of materials over the calculation. This will account for measurement errors and wasted resources.

Use the calculator below to determine the number of balusters or spindles needed.

Baluster or Spindle Measurement is in inches.

Note: A gap length of 4 inches is the maximum legally permitted.

Total Linear Feet Of Railing
* Required
Post Type
Total Posts
Baluster/Spindle Type
Spacing Between Balusters

Installation Begins with the Baluster Spacing Code


Before getting started on your DIY railing installation, take a look at these tips. You can never be too prepared, after all. Below, you’ll find information on the Baluster Spacing Code, requirements for installation, tools you may need, and a baluster calculator for more complicated installations. If you need a visual aid, we also have an array of baluster installation videos available to help you out.

First off, It’s a good idea to take a look at the Baluster Spacing Code before getting to work. In most instances, the gaps between the balusters (also called spindles) should not be greater than 4”.

Four inches is equal to 101.6 millimeters; many building inspectors carry a 100 mm or 4-inch ball for measurement that should barely fit through the space between the guard infill components. The maximum space between each 2-inch baluster should not exceed 99 mm, which leaves three 2-inch balusters per foot.

Some spindles connect directly to the decking, while others are secured to a bottom rail.

Bottom railings, too, should be 4” inches or less away from the deck surface. Local building departments may enforce this code, even if no children are in the home.

Spindle and Baluster Calculator

Do Indoor and Outdoor Stairs Require Railings and Balusters?


Yes. Guards must be installed on any stairs that exceed 30” above the ground. Guards, spindles, or balusters must be 34” to 38” when measured from the nose of a 10-inch deep tread. Interior stairwells require that anything over 2 steps or 3 risers would need a rail.

Balusters, or other options of vertical guards that support a handrail, should be able to support 50lbs over a 1-square-foot area. This is a 125-pound minimum testing force. The strength depends on the posts. The supporting posts or Newel Posts should be no farther apart than 6’ on a deck and 5.5’ on steps.

International Residential Code (IRC) Regulations for Deck Spindles


Local building departments may require closer post spacing. These agencies may also mandate which bolts or screws can be used so that the rail supports 200lb. of pressure. Be sure to check with your local safety codes before installing anything.

Railing safety codes dictate that decks, patios, landings, stairs, ramps, or walking surfaces above 30” off the ground need guardrails and vertical guards that are at least 36” high to prevent accidents at home. According to the International Residential Code (IRC), these regulations apply to houses that are 3 stories or smaller.

On the other hand, apartment buildings and commercial properties require 42” high guardrails from deck surface to the top of the rail.

Whether you want to make an old deck safe from falls and railing collapses, or you want to install new pickets or spindles, here are a few tools and tips will make the job go easier. 

Tools You May Need for Installing Your Balusters


    • 4 ft level
    • Combination square
    • Cut spacers
    • Drill and bits
    • Framing hammer
    • Framing square
    • Handsaw
    • Jigsaw
    • Miter saw
    • Safety goggles
    • Socket wrench and socket set
    • Tape measure

Where to Buy Spindles and Wood Deck Balusters


Consider S&L Spindles for all your spindle needs. Our team of experts can help with any questions you may have, and our broad selection of spindle products is readily available for browsing. Take a look, and tell us what you think!