Baluster Spacing Calculator

How to Measure Between Newel Posts

1. Measure at the floor, where the balusters will sit.
2. Hook your tape on the inside face of one newel post and measure to the inside face of the next one. If the railing ends at a wall, measure to the wall.
3. Measure each section of railing on its own. A balcony with a newel in the middle is two runs.
4. Pick your baluster width. Use the square or round part at the bottom, not the base shoe.

How to Lay Out Your Balusters

1. Make your first mark the calculator gives you, measured from the inside face of the left newel. That mark is the center of your first baluster.
2. Keep your tape hooked on the same newel and mark every number on the list. Measuring mark to mark adds up small errors.
3. Your last mark should be the same distance from the right newel as your first mark is from the left. If it is, your layout is even.
4. Transfer each mark up to the handrail with a level so every baluster stands plumb. See how to drill holes for balusters.

Spacing Balusters on Stairs

On stairs, lay out balusters one tread at a time. Most stairs with a 10″ to 12″ run take 3 balusters per step, which keeps them under 4″ on center.

• Line up the front face of the first baluster with the face of the riser below it.
• Space the rest evenly behind it. The calculator gives you every mark, measured from the front edge of the tread.
• With equal spacing on each step, the gap from the last baluster on one step to the first baluster on the next is the same as all the others.
• Make sure the back baluster clears the nosing of the step above.

How the Math Works

Here’s a 10′ (120″) balcony with 1/2″ iron balusters:

1. Add one baluster width to the length: 120″ + 1/2″ = 120-1/2″.
2. Divide by 4″ (the most on-center spacing we recommend) and round up: 120-1/2″ ÷ 4″ = 30.1, so 31 spaces.
3. One less than the spaces is your baluster count: 30 balusters.
4. Divide again to get exact spacing: 120-1/2″ ÷ 31 = 3-7/8″ on center.
5. Subtract the baluster width to get the gap: 3-7/8″ − 1/2″ = 3-3/8″, under the 4″ code limit.
6. First mark = gap + half a baluster: 3-3/8″ + 1/4″ = 3-5/8″ from the newel.

The gap at each newel matches the gap between balusters, so the railing looks even from end to end.

Baluster Spacing and Building Code

Most U.S. building codes, based on the International Residential Code (IRC), require that a 4-inch sphere cannot pass through any opening in the railing. Keeping balusters at 4″ on center or less keeps you under that limit with any baluster width. Local codes vary, so check with your building department before you install.