Fence Picket Spacing Calculator: How Many Pickets

This fence picket spacing calculator works out the exact gap (or picket width) for a given fence section: enter the total run length, picket width, and number of pickets, and you get the spacing between pickets, the number of pickets needed, and the total material length. It also lets you work backwards—if you have a desired gap, it tells you how many pickets fit.

Formula

For a fence section with a total length L (in feet), picket width w (in inches), and number of pickets n, the gap g between pickets (in inches) is:

g = (L × 12 – n × w) / (n – 1)

All units must match: convert the run length to inches (multiply feet by 12), then subtract the total width taken by all pickets (n × w). The remaining space is divided by (n – 1) because there is one fewer gap than pickets. For example, with 20 pickets there are 19 gaps.

If you know the desired gap instead, the number of pickets needed is:

n = ceil((L × 12 + w) / (w + g))

Here ceil rounds up to the next whole number, because you can’t use a fraction of a picket. The +w accounts for the extra picket at the end of the run.

Worked Example

Using the default values from the calculator: a 100-foot run, 5.5-inch pickets, and 20 pickets.

1. Convert run to inches: 100 ft × 12 = 1200 in
2. Total picket width: 20 × 5.5 = 110 in
3. Space left for gaps: 1200 – 110 = 1090 in
4. Number of gaps: 20 – 1 = 19
5. Gap per space: 1090 / 19 = 57.37 in

That gap is about 4 feet 9 inches—far too wide for a typical privacy fence, but the math is correct. The calculator shows 57.37 in (rounded to two decimals). For a real fence you would either increase the number of pickets or use a smaller gap.

How to Choose Picket Spacing

The right spacing depends on the fence’s purpose:

• Privacy fence: gaps are usually 0 to 0.5 inches. Many builders set pickets tight or with a 1/8-inch gap to allow for wood movement.
• Decorative or semi-private: gaps of 1 to 3 inches are common, often matching the picket width for a uniform look.
• Livestock or pet fence: gaps must be small enough to prevent animals from squeezing through—typically under 4 inches for dogs, under 2 inches for small pets.
• Airflow or view: larger gaps (4–6 inches) work for wind breaks or boundary markers.

Also consider local building codes, which may limit fence height or require specific gaps for pool safety. Always check with your local authority before building.

Common Mistakes and How to Avoid Them

• Mixing units: Forgetting to convert feet to inches is the most common error. Always multiply feet by 12 before dividing.
• Confusing gaps and pickets: The number of gaps is always one less than the number of pickets (unless the fence ends with a gap, which is unusual).
• Rounding too early: If you round the gap to the nearest 1/8 inch, the cumulative error over 20 pickets can be several inches. Keep full precision until the final layout.
• Ignoring post width: This calculator assumes the run length is the space between posts (inside to inside). If you measure from post center to center, subtract the post width first.
• Assuming pickets are exactly the same width: Wood can vary by 1/8 inch or more. Measure a sample of your actual pickets.

Comparison: Even Gaps vs. Panel-Based Layout

Two common layout methods are even spacing and panel-based spacing.

• Even spacing: The gap is identical between every pair of pickets. This is what the calculator does. It looks clean and is easy to calculate, but it can leave awkward gaps at the ends if the run length isn’t a multiple of (picket width + gap).
• Panel-based: You build a fixed panel (e.g., 8 feet wide) with a set number of pickets, then repeat that panel. This is simpler for prefabricated sections, but the spacing may vary slightly from panel to panel if the run length isn’t a multiple of the panel width.

For most DIY fences, even spacing is easier to achieve with a simple jig or spacer block. For long runs, panel-based can be faster because you can build sections on the ground.

Cost and Material Considerations

Picket spacing directly affects material cost. The number of pickets per 100 feet of fence can vary dramatically:

• With 5.5-inch pickets and 0.5-inch gaps: about 200 pickets (100 ft × 12 / 6 = 200).
• With 5.5-inch pickets and 3-inch gaps: about 141 pickets (100 ft × 12 / 8.5 ≈ 141).
• With 5.5-inch pickets and 6-inch gaps: about 104 pickets (100 ft × 12 / 11.5 ≈ 104).

More pickets mean more material, more nails or screws, and more labor. But wider gaps can reduce privacy and may not meet local codes. Always balance cost against function.

Safety and Installation Tips

• Wear gloves and eye protection when cutting pickets.
• Use galvanized or stainless fasteners to prevent rust and staining.
• Set posts in concrete below the frost line in cold climates to prevent heaving.
• Keep pickets at least 2 inches above the ground to avoid rot and allow for air circulation.
• If children or pets are present, ensure gaps are small enough to prevent head entrapment (typically under 4 inches).
• Check for underground utilities before digging post holes—call your local utility locator service.

Frequently Asked Questions

What is the standard gap between fence pickets?

There is no universal standard. For privacy fences, gaps are often 0 to 0.5 inches. For decorative fences, 1 to 3 inches is common. The gap you choose depends on your need for privacy, airflow, and local codes.

How do I measure the run length for a fence?

Measure the distance between the inside faces of the two end posts (or between the center of the posts if you will attach pickets to the outside face). If you measure from post center to center, subtract half the width of each post to get the actual run length for pickets.

Can I use this calculator for metal or vinyl pickets?

Yes, the math works for any material. Just enter the actual width of the picket (or slat) and the total run length. For metal or vinyl, the picket width is usually uniform, so the calculation is even more precise.

What if my fence has a gate?

Treat the gate opening as a separate run. Measure the width of the gate opening and enter that as the run length if you want to match the picket spacing on the gate. Otherwise, you can ignore the gate and just build it with the same picket width.

How do I convert the gap from inches to a fraction for a tape measure?

Multiply the decimal by 16 to get the nearest 1/16 inch. For example, 0.375 inches × 16 = 6, so 0.375 in = 6/16 in = 3/8 in. Use a spacer block cut to that size for consistent gaps.

Why does the calculator give a huge gap for my 100-foot run with 20 pickets?

Because 20 pickets over 100 feet is only about one picket every 5 feet. That leaves a massive gap. For a typical privacy fence, you would need roughly 200 pickets (with 5.5-inch pickets and 0.5-inch gaps). Adjust the number of pickets until the gap looks reasonable.

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in total | Total run length | ft | 100 | 0
in pw | Picket width | in | 5.5 | 0
in n | Number of pickets | - | 20 | 0
out gap | Gap between pickets | in | (total * 12 - n * pw) / (n - 1) | 2
out pickets | Pickets needed (even gap) | - | ceil((total * 12 + pw) / (pw + gap)) | 0
out material | Total picket material | ft | n * pw / 12 | 2