How to Calculate Spindle Spacing

Updated February 21, 2017

Structures with spindles such as decks and stair units are usually subject to building code requirements that dictate the maximum amount of space allowed between each spindle. Maximum spindle spacing limits are designed to prevent children from getting their heads stuck between spindles or falling off of high decks or stair units. Codes, available from county building departments, also specify the number of spindles allowed on each project calling for them. To calculate spindle spacing, a mathematical formula will help you build to code and space each spindle correctly.

Measure the length of the structure that requires spindles such as a deck rail or stair rail. This will help you determine how many spindles you will need according to the building code.

Obtain a copy of the building codes in your area and retrieve the maximum gap size figure. Subtract the maximum gap size figure from the length of the rail. This number is then divided by the length. Round your answer to the nearest whole number to determine how many spindles you will need. For example, if your rail is 266 cm (105 inches) and gap maximum 12 cm (5 inches) and spindle width 4 cm (1.5 inches), the formula in centimetres would be (266 - 12) / (12 + 4) = 25.1 cm. Or in inches (105 - 5) / (5 + 1.5) = 21.5 inches. Rounding to the nearest whole, give you 25 and 22 required spindles respectively.

Calculate the space between spindles. Start by multiplying the width of each spindle by the number required. The answer is subtracted from the rail length to determine the total gap space of the spindles. The formula looks like 22 x 1.5 = 33.105-33 = 72.

Calculate the space between each spindle. This is done by dividing the amount of total gap space by the number of spindles. For example 72 / 22 = 3.27. The answer represents the maximum amount of space, in inches, allowed between each spindle.


Always refer to building codes before you begin.


Always display your building permit in plain sight. Wear protective eye wear when cutting wood.

Things You'll Need

  • Pencil
  • Measuring tape
  • Calculator


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About the Author

Jim Hagerty is a writer and journalist who began writing professionally in 1996. He has had articles published in the "Rock River Times," "Builder's Journal" and various websites. He earned a Bachelor of Science in public relations and journalism from Northern Michigan University in Marquette.