Baluster Calculator

Baluster Calculator for Deck and Stair Railings

The Baluster Calculator counts how many spindles (balusters) you need between railing posts. Enter railing length, post count, post width, baluster width, and center-to-center spacing. The tool rounds up to a whole baluster count and flags spacing that may exceed common code limits.

Baluster spacing formula

Effective railing span minus post width, divided by one baluster plus one gap:

$$n = \left\lceil \frac{L - n_p \times w_p}{w_b + s} \right\rceil$$

Where $L$ is railing length, $n_p$ is number of posts, $w_p$ is post width, $w_b$ is baluster width, and $s$ is spacing between balusters.

Building code spacing

Many residential codes limit baluster spacing to 4 inches (99 mm) so a 4-inch sphere cannot pass through. Always verify your local jurisdiction before finalizing a design.

Related tools: Fence Calculator, and Stair Calculator.

Frequently Asked Questions

What is the maximum baluster spacing allowed?

In many US areas the limit is 4 inches (99 mm) clear space. Some jurisdictions are stricter. Check local deck and stair guardrail codes.

How many extra balusters should I buy?

Order 10% to 15% more than calculated to cover miscuts, breakage, and future repairs. The calculator shows a recommended order quantity with 15% buffer.

Do end posts count in the post total?

Yes. Include every post that occupies space along the railing run, including corner and end posts.

What if my balusters are irregular shape?

Use the widest part of the baluster profile as the width input so spacing stays code-compliant at the widest point.

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