Calculate how many balusters are needed for a deck or stair railing. Select the total railing length, the number and size of posts, and the size of baluster.
How to Calculate the Number of Railing Balusters You Need
Estimating how many balusters are needed for a railing by using the calculator above. If you’re building a deck check out our deck flooring calculator to estimate the flooring needed for your deck. 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.
Steps to Estimate Railing Baluster Quantities
The first step to estimating the quantity of balusters for a railing is to measure the length of the railing. 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 3.5″(4×4) postswould have a total length of 120″ – (3 x 3.5″) = 120″ – 10.5″ = 109.5″.
The next step in estimating the number of balusters needed is to add the thickness of the baluster to the maximum space between the balusters to get the combined baluster and spacing width. For example, a 1.5″(2×2) thick baluster with a 4″ spacing between the balusters would have a combined width of 4″ + 1.5″ = 5.5″.
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 5.5″, eg. 109.5″ / 5.5″ = 19.9. Since we can’t add partial balusters the solution should be rounded up from 19.9 to 20.
Baluster Quantity Calculation Tips
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.
In most areas the code requires the maximum spacing between balusters to be 4″ or less for safety. Decks Direct notes that the maximum 4″ baluster spacing is part of the International Residential Code. 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.