Carpentry
Fence Picket Spacing Calculator
Stop doing trial-and-error math on your railing. Enter your total span and picket width to get the exact, uniform gap size required for a perfect layout.
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How to Use the Spacer Block Method
The fastest way to install dozens of pickets perfectly isn't by measuring and marking every single one—it's by using spacer blocks.
1. Cut Your Blocks
Use the "Gap Size" calculated above and cut two blocks of scrap wood to that exact length. Make sure your cuts are perfectly square.
2. Stack and Shoot
Place your spacer blocks tightly against the post (one at the top rail, one at the bottom). Press your first picket tight against the blocks and fasten it. Move the blocks over, and repeat the process across the entire span.
The Math Behind Picket Spacing
Calculating the perfect layout so the pickets are evenly spaced without any ripped boards is a classic layout problem. Here is how the calculator works it out:
| Calculation | Formula | Notes |
|---|---|---|
| Number of Pickets | (Total Span + Target Gap) ÷ (Picket Width + Target Gap) | We add a phantom gap to the total span because every picket essentially brings its own gap, plus one extra gap at the end. The result is rounded to the nearest whole number. |
| Remaining Space | Total Span − (Number of Pickets × Picket Width) | Once we know the number of pickets, we subtract their combined width from the span. What's left over is pure empty space. |
| Exact Gap | Remaining Space ÷ (Number of Pickets + 1) | We divide the pure empty space by the number of gaps. Because there is a gap at both ends, the number of gaps is always one more than the number of pickets. |
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Frequently Asked Questions
How big should the gap between fence pickets be?
For privacy fences, gaps are usually 0 to 1/4 inch0 to 6 mm. For semi-privacy, a 1/2 inch to 1 inch12 mm to 25 mm gap is common. For traditional picket fences, a 1-1/2 inch to 2 inch38 mm to 50 mm gap provides a classic look. Ultimately, it is entirely up to your personal aesthetic preference.
How do you calculate equal spacing for pickets?
To calculate equal spacing, you add the width of one picket to the total span, then divide by the target gap plus the picket width. This gives you the number of spaces. You then subtract the total width of all pickets from the span and divide by the number of spaces to find the exact gap size.
Do I measure center-to-center or edge-to-edge?
The visual space between the boards is the physical edge-to-edge gap. However, when laying out and installing the pickets, marking center-to-center measurements on your rails is often the easiest and most accurate method.
What is the easiest way to install evenly spaced pickets?
Calculate your exact gap size using this calculator, then cut two wooden spacer blocks to that exact length. When installing, simply place the spacer blocks against the previous picket, press the next picket against the blocks, and fasten it.
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