Baluster Calculator

Calculate the Perfect Space Between Railing Spindles

Use the calculator to figure out how many balusters or spindles you'll need for a section of deck railing. We broke it down to 4, 6, and 8 feet sections. Example: My railing section between the deck post is 6 feet. I'm using 2 X 3 spindles so I need 12 spindles. This calculator also works for balusters.

Measurements are in inches.

Gap Length:

Railing Length:


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.

You may need:

  • 4 ft level
  • Adjustable crescent wrench
  • Assorted screwdrivers
  • Baluster calculator
  • Combination square
  • Cut spacers
  • Drill and bits
  • Earplugs
  • Framing hammer
  • Framing square
  • Handsaw
  • Jigsaw
  • Knowledge of building regulations and community-specific building codes
  • Miter saw
  • Nail pouch
  • Pencil
  • Plumb bob
  • Power saw
  • Pry bar
  • Safety goggles
  • Sawhorses
  • Socket wrench and socket set
  • Tape measure
  • Torpedo level

What is the Baluster Spacing Code?spacing between baulsters and spindles

Guards are building components on open sides of any elevated walking surface. Sometimes spindles, panel fillers, pickets, and balusters are referred to as “vertical guards” or “guard infill components.” Benches, however, aren’t guards.

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.

How Much Space Should Be Between Balusters or Spindles?

Not all pickets, spindles, and balusters follow the 4” rule. Widths play a factor. Six-inch balusters, spindles or pickets may be placed 6” or more apart.

Be sure to check with your local regulatory agency for exact spacing requirements as they may still require 4” on 6” spindles.

Do All Decks Require Railings?

No. Low-rise decks, floating decks, and ground level decks are exempt from some guardrail requirements and may not require building permits.

However, if desired, decks below 30” off the ground can still have pickets, balusters, or spindles installed.

Each would need to meet the 4” baluster spacing code. Many builders install balusters, pickets or spindles 4” on center to comply with the requirement.

Do Indoor or Outdoor Steps Require Railings and Balusters?

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.  

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.