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Shadow Box Fence Calculator

See how many pickets go on each side of a shadow box fence, how much they overlap, and everything else on the material list.

New cedar privacy fence and gate along a backyard lawn
Units
Measure by
ft
corners

Where the fence turns.

Gates
4 ft gate
Shadow box fence details
ft
ft

Center to center, at most.

Picket width
in
Post size
in

Follows the height. Go deeper if your frost line is lower.

Hole diameter: 10.5 in, three times the post width.

Enter a fence length, draw the line on the map, or add sides to see your materials.

How the shadow box fence calculator counts

A shadow box fence has pickets on both sides of the rails, alternating. On each side the pickets are spaced a little less than one picket width apart, and the pickets on the other side sit behind those gaps. Looking straight at it you cannot see through, but air passes between the two layers at an angle.

Each side is a spaced picket run, so the calculator counts one side and doubles it:

Pickets per section = 2 × (section length + gap) ÷ (picket width + gap), each side rounded up

The overlap and the see-through gap come from the same two numbers:

Overlap on each edge = (picket width − gap) ÷ 2

If the gap is wider than the picket, the overlap turns negative: that much stays open beside every picket and you can see through the fence. The panel beside the material list shows this as you change the gap.

Posts go at every corner, end and gate, and sections are no longer than your post spacing. Rails follow the height: two per section up to 4 ft, three up to 6 ft and four above. Pickets, rails and nails get 10% extra for waste, the allowance Inch Calculator recommends.

A worked example

The calculator opens on 150 ft of 6 ft shadow box fence with two corners and one 4 ft walk gate, using 1x6 pickets with a 3 1/2 in gap on each side. The gate splits one of the three 50 ft sides into two 23 ft stretches, which leaves 146 ft of fence.

  • Posts at 8 ft at most give 3 sections of about 7.67 ft in each 23 ft stretch and 7 sections of about 7.14 ft on each 50 ft side. That is 20 sections on 22 posts.
  • A 1x6 picket is 5 1/2 in wide, so one picket plus one gap is 9 in. A 7.67 ft section (92 in) takes (92 + 3.5) ÷ 9 = 10.6, so 11 pickets per side and 22 per section. A 7.14 ft section takes 10 per side, 20 per section.
  • 6 × 22 + 14 × 20 = 412 pickets: 206 on each side. With 10% extra, buy 454 pickets.
  • The overlap is (5.5 − 3.5) ÷ 2 = 1 in on each edge, so the see-through gap looking straight on is zero.
  • Three rails per section is 60, or 66 rails, and 91 bags of 50 lb fast-setting concrete for the 22 posts in 42 in holes.

Why the gap is a bit narrower than the picket

The Extreme How-To shadowbox build cuts its spacer block "slightly narrower than the width of the fence boards", so the pickets on the two sides overlap a little. With 5 1/2 in pickets, the 3 1/2 in default gap gives 1 in of overlap on each edge. A 4 1/2 in gap would give 1/2 in,, and at 5 1/2 in the two sides would just meet edge to edge.

The same guide builds a 6 ft fence with the bottom rail 10 in above grade and the rails 23 in apart, on posts "usually 6 to 8 feet on center". The calculator uses 8 ft, the top of that range. Set a shorter post spacing if you want stiffer sections.

Board sizes are actual widths. ProWood lists a 1x6 at 3/4 by 5 1/2 in and a 1x4 at 3/4 by 3 1/2 in. With 1x4 pickets, keep the gap under 3 1/2 in to keep the overlap.

Shadow box or board on board?

Both use two layers of boards and more wood than a plain privacy fence. On the example fence, board on board with a 1 in overlap takes 432 boards and shadow box 454, against 359 for a single layer.

The difference is where the second layer goes. Board on board stacks both layers on the same side of the rails, so the fence has a front and a back. Shadow box puts one layer on each side, so both neighbors see the same face, and the rails sit between the layers where neither side sees them. See the board on board fence calculator for that style's overlap math.

What does a shadow box fence cost?

Fixr puts a shadowbox fence at $19 to $39 per linear foot installed. For the 146 ft example that is $2,774 to $5,694, plus $200 to $600 for a wood gate, HomeAdvisor's range. Finishing costs more than on a single sided fence because both faces show. HomeAdvisor gives $4 to $14 per foot to paint or stain a shadowbox fence, against $2 to $10 for a privacy fence. The fence stain calculator works out gallons for both faces.

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