How to Calculate Deck Baluster Spacing

Deck balusters ensure a sturdy wood railing – that is, if they're spaced correctly. Learn how to use different methods to calculate spacing. Some methods will give you an uneven gap at the end, and others will be more precise. Remember to take post spacing into consideration as well. Posts are the anchors that will provide that extra bit of security and strength. As a general matter, it's important to keep in mind that building codes allow a minimum gap of 4 inches between balusters. With the right materials, you can begin working on your do-it-yourself deck project.

Thai-style seating on balcony in garden house
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How to Calculate Deck Baluster Spacing

Uneven? No Problem

If you're okay with having a gap at one end of the guardrailing, then you can simply space the balusters 4 inches on center across the entire run of guardrail. Make sure the opening at the end is less than 4 inches so as not to leave a large end gap. This may not be the most attractive option, but it is relatively straightforward.

A More Precise Measurement

Say each baluster is 1.5 inches. Now, multiply that by the number of balusters – let's say 13 – to total 19.5 inches. This is the amount of space the balusters themselves (without spaces) will take up from post to post. Subtract 19.5 inches from 68.5 inches, which is the total inches between posts. You will end up with 49 inches of empty space between posts. Divide 49 inchesby 14 spaces. Note that there will always be one more space than baluster. The total space between each baluster is 3.5 inches. For accuracy, use a space – in this case, one that's 3.5 inches. Once you've calculated the correct baluster spacing, be sure to mark the spots on the top and bottom rails so you can identify where the balusters will be installed. For a precise measurement, feel free to use an online calculator. Input the total railing length, the number and size of posts and the size of the baluster.

Let’s Not Forget About the Posts

When constructing a railing, it's important to take posts into consideration, as well as balusters. Posts are the anchors that are generally taller than the balusters, and most building codes allow no more than 68.5 inches between porch railing posts. Posts are measured using the maximum space allowed, which is 68.5 inches. This number is divided by the baluster space calculation – let's say 5.5 inches – which will give you a total of 12.45 inches. Therefore, you will need 13 balusters and there will be 14 spaces.


C.H. Bodian

C.H. Bodian

Caroline is a writer from NYC. Her writing has appeared in L.A. Weekly, Elle.com, New York Magazine, Marie Claire and The Huffington Post. She produces content on women's health/wellness, design/DIY and business for companies such as Meredith Corporation, Leaf Group and the business school, Hautes Études Commercials Paris. She's a former Production Associate and blogger at Show of Force, the production company behind Nicholas Kristof's and Sheryl WuDunn's, Half the Sky.