Shadow Box Fence Picket Spacing Calculator
Enter the clear width of one fence bay, the actual board width, and the overlap you want. The calculator selects the smallest whole front-face count that meets that overlap, then gives matching rear-face marks and material quantity.
Same-face center spacing (in)9.05
- Front-face pickets per bay
- 11
- Rear-face pickets per bay
- 10
- Clear gap between same-face pickets (in)
- 3.55
- Achieved overlap on each edge (in)
- 0.97
- Pickets required before waste
- 21
- Pickets to purchase
- 24
- Front and rear layout marks
- Front: 0 in, 9.05 in, 18.1 in, 27.15 in, 36.2 in, 45.25 in, 54.3 in, 63.35 in, 72.4 in, 81.45 in, 90.5 in. Rear: 4.525 in, 13.575 in, 22.625 in, 31.675 in, 40.725 in, 49.775 in, 58.825 in, 67.875 in, 76.925 in, 85.975 in.
Front marks are left-edge marks from one bay boundary; rear marks are centered between adjacent front marks.
Each bay is calculated independently, so measure unequal bays separately.
The whole-picket count creates noticeably more overlap than requested; check the displayed spacing before fastening.
How to use this calculator
- Measure the clear span available to the pickets in one bay, not the post-to-post nominal distance.
- Measure several pickets and enter their actual face width rather than their nominal size.
- Choose the minimum amount a rear picket should overlap each neighboring front picket.
- Enter the number of bays only when they have the same clear width, then add a material allowance.
- Mark every position from the same bay edge and test-fit representative boards before fastening.
How shadow box picket spacing is calculated
A shadow box fence has front pickets at regular intervals and rear pickets centered behind the openings. The front face begins with a picket at the left bay boundary and ends with one at the right boundary. That means the calculator works from the available span back to a whole number of front pickets, rather than starting with an arbitrary gap.
Let L be the clear bay width, W the actual picket width, and O the requested overlap at each edge. The widest permitted same-face pitch is Pmax = 2 × (W − O). The front count is N = max(2, ceil(1 + (L − W) ÷ Pmax)). Once that whole count is chosen, the exact pitch is P = (L − W) ÷ (N − 1).
The clear gap between front pickets is G = P − W, and the overlap of a rear picket behind either neighboring front picket is A = W − P ÷ 2. There is one rear picket in every opening, so a bay has N − 1 rear pickets and 2N − 1 pickets in total. For equal bays, multiply that total by the bay count, then round the allowance upward: purchase = ceil(required × (1 + waste ÷ 100)).
Making the layout marks
Use one consistently measured bay edge as zero. Front left-edge marks are 0, P, 2P ... (N − 1)P. Rear left-edge marks are halfway between them: 0.5P, 1.5P ... (N − 1.5)P. The mark list is calculated from the full-precision pitch, not by repeatedly adding a rounded spacer measurement. A story pole or pair of spacer blocks made from a test layout can make those marks easier to transfer to each rail.
What affects the result most
Actual board width and the requested overlap have the largest effect. A small change can force one additional front picket into the bay, making the achieved overlap larger than the target. Very narrow same-face gaps also leave little room for boards that vary in width, cup, or swell. Measure several boards from the bundle and dry-fit a section when the result is tight.
What this calculator leaves out
This is a horizontal picket-layout calculation. It does not design posts, rails, fasteners, gates, caps, post covers, cuts, or structural resistance to wind. It also assumes straight, uniform-width pickets and equal staggering on both faces. Check local height, setback, and wind requirements separately before building.
Worked example
For a 96 in clear bay using 5.5 in actual pickets and a 0.5 in minimum overlap, the maximum pitch is 2 × (5.5 − 0.5) = 10 in. The front count is ceil(1 + (96 − 5.5) ÷ 10) = 11. The exact pitch is 90.5 ÷ 10 = 9.05 in, leaving a 3.55 in same-face gap and producing 0.975 in of overlap on each edge.
That bay uses 11 front pickets and 10 rear pickets, or 21 total. Three equal bays need 63 pickets before allowance. With 10% extra material, the purchase quantity is ceil(63 × 1.10) = 70 pickets. The first front marks are 0, 9.05, and 18.10 in; the first rear marks are 4.525 and 13.575 in.
Common questions
How is shadow box spacing different from ordinary fence picket spacing?
An ordinary single-face layout only needs a consistent gap between adjacent pickets. A shadow box layout also needs each rear picket centered behind a front-face opening and overlapping both adjacent front pickets. That two-face relationship is why the pitch is based on the overlap as well as the board width.
How much should shadow box fence pickets overlap?
The useful amount depends on the look you want, the board width, and expected movement. Enter the minimum overlap you need; the calculator may show more because a bay must use a whole number of pickets. Test the result with actual boards before fastening the whole bay.
Why are there fewer pickets on the rear face?
The rear face fills the openings between front pickets, not the two outside bay boundaries. If the front face has N pickets, it creates N minus 1 interior openings. One centered rear picket goes behind each opening.
Where should the first front and rear pickets start?
Start the first front picket at the chosen bay boundary, which is the zero mark. Start the first rear picket one-half of the same-face pitch from that edge. Keep every mark referenced to the same edge instead of adding rounded dimensions one after another.
Should I use nominal or actual picket width?
Use the actual face width. Nominal lumber names do not reliably describe the width of the boards in your bundle, and wood pickets can vary within the same stack. Measure several representative boards and use a conservative width when the gaps are tight.
How should I handle fence bays with different widths?
Calculate each different clear bay separately. Carrying a pitch or board count from a full bay into a shorter one can change the overlap and make the end layout look uneven. A story pole can still be useful within each group of equal bays.