Question 1

How do I space balusters evenly?

Accepted Answer

Balusters divide a span into one more gap than there are balusters. Work out the smallest count whose resulting gap clears 4 inches, then space them at that gap plus one baluster width on centre. The calculator does this for you.

Question 2

What is the maximum gap between balusters?

Accepted Answer

Four inches. IRC R312.1.3 states that a 4-inch sphere must not pass through any opening in a guard. The rule exists so that a small child cannot fit through, and inspectors genuinely carry the sphere.

Question 3

Do balusters need to be 4 inches apart or 4 inches on centre?

Accepted Answer

The gap between them must be under 4 inches — not the on-centre spacing. With 1.5-inch balusters, a 4-inch gap means 5.5 inches on centre. Confusing these is the most common failure at inspection.

Question 4

How many balusters do I need for a 6-foot railing?

Accepted Answer

A 72-inch clear span with 1.5-inch balusters needs 14, giving gaps of just under 3.9 inches. Adding a baluster is always the fix for a gap that is over — never widen the spacing.

Question 5

What is the 6-inch sphere rule on stairs?

Accepted Answer

At the triangular opening formed by the tread, the riser, and the bottom rail of a stair guard, a 6-inch sphere must not pass. Everywhere else on the guard, the 4-inch rule still applies.

Question 6

How tall does a deck railing need to be?

Accepted Answer

Thirty-six inches minimum for residential guards under the IRC, measured from the walking surface. Some jurisdictions require 42. Stair handrails are separate and sit between 34 and 38 inches above the nosings.

Question 7

Should I start with a baluster or a gap at the post?

Accepted Answer

A gap. The pattern is gap-baluster-gap-baluster-gap, which is why there is always one more gap than baluster. Starting with a baluster against the post leaves an uneven end and usually an oversized gap at the other.

Question 8

Can I use cable railing instead of balusters?

Accepted Answer

Yes, and the same 4-inch rule applies to the openings between cables. Cable needs enough tension to stay within it — typically 3-inch spacing with intermediate supports every 3 to 4 feet, since cable deflects when pushed.

Baluster Spacing Calculator

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