Baluster Calculator

Most building codes (IRC R312, IBC 1015) require that the space between balusters does not exceed 4 inches (102 mm). This is to prevent a 4-inch sphere from passing through, which protects children from getting their heads stuck. Some areas may have different requirements - always check local codes. For commercial buildings, the requirement may be more strict at 4-inch maximum spacing measured at the narrowest point between balusters.

While often used interchangeably, balusters are the vertical posts that support the handrail in a railing system. Spindles typically refer to turned or decorative balusters commonly used in staircases. Pickets are vertical members in fencing rather than railing. All serve similar functions but may have different style characteristics. The calculation method for spacing them evenly is the same regardless of terminology.

The 4-inch maximum spacing rule applies to both stairs and decks/landings. However, on stairs, balusters are typically installed at an angle following the stair slope. The horizontal measurement between balusters on stairs is what matters for code compliance - the diagonal spacing along the stair angle will be slightly larger. For stairs, measure the horizontal gap at the tread level to ensure code compliance.

To center balusters evenly: First, install end posts. Measure the total railing length between posts. Add one baluster width to this length. Divide by the total number of balusters plus one. This gives you the center-to-center spacing. Subtract the baluster width to get the clear opening space. Always dry-lay a few balusters to verify spacing before final installation.