Baluster Calculator

Installation Begins with the Baluster Spacing Code

spacing between baulsters and spindlesBefore 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 or spindles should not be greater than 4”.

Four inches equates 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 or spindle should not exceed 99 mm; which leaves three 2-inch balusters or spindles per foot.

Some balusters and spindles connect directly to the decking; 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. This rule is important because the average diameter of a baby’s head is around 4”. Spacing the balusters at a proper distance may prevent small children from getting their heads caught.


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.  

Railing safety codes dictate 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 three-story or smaller houses.

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, spindles, or deck balusters, 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

Calculate the Perfect Space Between Railing Spindles

Balusters and spindles make up vertical guards that support handrails. The guards should be able to support 50 lbs. of pressure per square foot.

To determine the correct number of balusters for the guard, measure the length of the railing. Count the number of vertical guards and the measure the thickness of each. Multiple the number of balusters by the thickness. Subtract this number from the length of the railing.

Add the thickness of the baluster to the space between each of the guards. Four-inch spacing is standard in many areas. Combine the number balusters with the required spacing.

Divide the rail’s length by the area of the baluster and required spacing to determine the number of balusters. Any partial baluster calculations to round up to the next whole number.

Consider adding an additional 10% of materials over the calculation. This will account for measurement errors and wasted resources.

Baluster Calculator

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.

Calculator Settings:

Gap Length:

Railing Length:


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!