How to Calculate Baluster Spacing

Sketch the rails (horizontal top and bottom members) on a piece of paper. Measure the length of the rail, using a tape measure. Label the sketch with dimensions in inches. Mark the approximate center of the rails.

Check local building codes to determine the maximum distance between the narrowest parts of the balusters. Place two balusters parallel on a flat surface with the maximum allowable space between them. Mark the centers of the tops or bottoms of the balusters. Measure the distance between the centers of the balusters to determine the maximum allowable distances between the centers of the balusters.

Measure the width of the balusters. Add the width of the balusters to the desired space width between balusters. Spacing of the balusters depends not only on regional building safety codes, but also the desired appearance of the finished project. Plain sawn balusters, cut from 2 by 2-inch lumber, are often installed with 2-inch spacing. Spindles are typically spaced farther apart to draw attention to the fine detail of the individual spindle and to give a lighter, more airy overall feel to the architectural design. Decorative cut-out sawn balusters, such as those used in gingerbread architecture, are often spaced very closely.

Divide the length of the rails by the width of the balusters plus the desired space between the balusters. Round this to the nearest lower whole number. This number will tell you how many balusters you need to fill the space. If the number is even, the middle of the rail will have a space between balusters. If the number is odd, there will be a baluster centered to the length of the rail. When installing balusters, always start from the center of the rail and work outward so the spaces between the end balusters and posts are uniform. To make the space between the last balusters and the posts the same width as the spacing of the rest of the balusters, see Step 5.

Divide the length of the rails by the width of the balusters plus space, as in Step 4. Round this to the nearest lower whole number. This is how many balusters you need. Multiply the number of balusters by the width of the baluster and subtract this number from the rail's length. The difference is the area occupied by the spaces between the balusters. Divide this difference by the number of balusters plus one. The answer will be the width of the spacing needed to make all spaces, including the end spaces, uniform.