Baluster Calculator

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.

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

Baluster or Spindle Measurement is in inches.

Gap Length:

Railing Length:


Where to Buy Spindles and Wood Deck Balusters

Western Red Cedar and Pressure Treated Pine Options for Spindle Railing

24" to 48" options available on various turned balusters

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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.

Are Deck Spindles Required All Outdoor Structures?

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

Low rise deck  floating deck

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 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

  • 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