How to Calculate Deck Baluster Spacing

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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.

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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.

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Uneven? No Problem

If you're OK with having a gap at one end of the railing, 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.

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A More Precise Measurement

If you want the same spacing when building a deck, use a tape measure to check the measurements of each side of the deck and the width of each baluster. 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.

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You will end up with 49 inches of empty space between posts. Divide 49 inches by 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 spacer — in this case, one that's 3.5 inches wide. 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.

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Spacing for the Posts

Post spacing is also an important consideration when building a railing. The deck railing posts are taller than the balusters and anchor the railing. Most building codes allow a maximum of 6 feet between porch railing posts.

You'll need posts at each corner and at the top of the stairs. The remaining posts should be spaced evenly between the two posts without exceeding the maximum spacing allowed by local building codes. To calculate the number of posts, divide the length of each section by the maximum length allowed between posts, round up your answer, and take away 1. For example, for a 20-foot distance with a maximum of 6 feet between posts, divide 20 by 6 to get 3.33, round up to 4, and subtract 1 to get 3. You'll need to space three posts equally between the two posts on that side.

Once you know how many posts you need, you can calculate how far apart to position them so they're evenly spaced. You'll need to calculate the number of posts and spacing separately for each section to ensure the posts are evenly spaced.

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