Baluster Calculator

Calculate how many balusters you’ll need for a deck or stair railing by selecting the total railing length, the number and size of posts, and the size of the balusters.

Calculate baluster spacing and layout by entering the baluster size and the length of each section of the railing.

Layout Using:
The maximum safe/legal baluster spacing is 4" in most areas, always follow local building codes for safety.
The maximum safe/legal baluster spacing is 4" in most areas, always follow local building codes for safety.
Railing Sections
Length is the distance between the inside edge of each post.

Baluster Estimate:

Balusters Needed
Learn how we calculated this below

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How to Calculate How Many Railing Balusters You Need

Deck railing with evenly spaced balusters

You can estimate how many balusters you need for a railing using the calculator above or by following the steps below. If you’re building a deck, check out our deck flooring calculator to estimate the flooring needed for your deck.

Steps to Estimate Balusters and Spindles

The first step to estimating how many balusters you need for a railing is to measure the railing length. You will also need to identify the number of railing posts needed and the thickness of the posts.

To account for the post thickness, simply multiply the number of posts by the thickness, then subtract from the railing length. For example, a 10′ railing with 3 3½”(4×4) posts would have a total length of 120″ – (3 × 3½”) = 120″ – 10.5″ = 109.5″.

The next step in estimating the number of balusters needed is to add the thickness of the baluster or spindle to the maximum space between them to get the combined width. For example, a 1½” (2×2) thick baluster with a 4″ spacing between the balusters would have a combined width of 4″ + 1½” = 5½”.

The final step in finding how many balusters you need is to divide the railing length(minus the posts) from the first step by the combined baluster/spacing width from the second step.

For example, we would take the 109.5″ railing length and divide by 5½”, e.g. 109½” ÷ 5½” = 19.9. Since we can’t add partial balusters, round up the solution from 19.9 to 20.

It is a good idea to order about 10% additional materials to account for waste or measurement errors. This is a general rule of thumb for many construction projects.

How Far Apart Should Balusters Be Spaced?

In most areas, the code requires the maximum spacing between balusters to be 4″ or less for safety. International Residential Code requires a maximum baluster spacing of four inches.[1]

It is important to understand the building code in your area, and safety is an important consideration. We recommend a maximum spacing of 4″ between balusters for this reason.

Get a free deck installation estimate from a contractor in your area for pricing comparisons or if you’d like to hire your deck project out.


  1. Decks Direct, Baluster FAQs - Baluster Guide,