Picket Spacing Calculator
Enter the opening between posts, your picket width and the largest gap your code allows. Get the number of pickets, the exact equal gap, and a mark-out list you can scribe straight onto the rail.
Equal gaps, marked from one end.
Results update as you type. Inches take whole numbers, decimals or fractions, such as 3, 3.5 or 3 1/2.
Gaps are equal, including the gap at each post. Every gap is held at least 1/8 inch under your limit, so rounding the marks to 1/16 cannot push one over.
Lay it out once, from one post.
Measure the real opening
Measure between the posts as built, not off the drawing. Posts drift, and the layout is only as good as that number.
Hook your tape on one post
Every mark is the near edge of a picket, measured from the face of the first post. Marks taken from one end do not stack up error the way a spacer block does.
Check before you weld
Tack the first, middle and last picket, then try the gaps with a ball or a block cut to your code size before welding out the run.
The code tests gaps with a ball.
Guard openings are limited by a sphere test: if a ball of the stated size can pass through, the gap is too big. The International Residential Code (R312.1.3) uses a 4-inch sphere for guards. Wisconsin’s Uniform Dwelling Code, SPS 321.04(3)(a)3., uses a 4 3/8-inch sphere with 4 pounds of force for one- and two-family homes.
Commercial work falls under the building code, and stairs, cable infill and the triangle under a stair rail have their own limits. Enter the number your inspector uses.
Layout aid only. This tool spaces pickets. It does not design the rail. Post size, anchorage, top rail strength and rail height are separate requirements, and your local code and inspector have the final word.
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Our specialists are happy to answer your questions and help scope your project.