Fence Picket Calculator: Count & Spacing

This fence picket calculator works out how many pickets you need for a fence run and the exact gap between them. You enter the total fence length, the picket width, and the gap you want between pickets (or let it calculate an even gap), and it returns the number of pickets required plus the precise spacing. It handles both metric and imperial measurements, so you can work in feet and inches or meters and centimeters.

Formula

The core formula treats each picket plus one gap as a single repeating unit. If the fence length is L (in feet), the picket width is W (in inches), and the desired gap is G (in inches), the number of pickets N is:

N = ceil( (L × 12) / (W + G) )

Where ceil means round up to the next whole number. The actual gap is then recalculated to spread the leftover space evenly:

Actual gap = (L × 12 − N × W) / (N − 1)

All lengths are converted to inches first so the formula works for any unit combination. The result is the number of pickets for a straight run between two end posts.

Worked Example

Using the default values from the calculator: fence length = 100 ft, picket width = 5.5 in, desired gap = 2 in.

1. Convert fence length to inches: 100 × 12 = 1200 in
2. Add picket width and gap: 5.5 + 2 = 7.5 in per unit
3. Divide total length by unit: 1200 ÷ 7.5 = 160
4. Round up: 160 pickets
5. Actual gap: (1200 − 160 × 5.5) ÷ (160 − 1) = (1200 − 880) ÷ 159 = 320 ÷ 159 ≈ 2.01 in

So you need 160 pickets, and the real gap will be about 2.01 inches – essentially the same as the desired 2 inches because the numbers divide evenly. When they don’t divide evenly, the calculator shows the adjusted gap so you know exactly what to set.

How to Measure Your Fence Run

Measure the total length of the fence line between the inside faces of the two end posts. Do not include the posts themselves in the picket run – pickets typically attach to the rails between posts. For a fence with intermediate posts, measure each section separately and add the picket counts together, because the gap at each post may need adjustment.

• Use a tape measure along the top rail, not the ground, for accuracy on slopes.
• Measure in inches for the most precise result, then convert to feet for the calculator.
• If the ground is uneven, the horizontal distance matters, not the slope distance.

Choosing Picket Width and Gap

Picket width is usually determined by the material you buy – common sizes are 3.5 in, 4 in, 5.5 in, and 6 in. The gap is a design choice, but it affects both privacy and cost. Smaller gaps mean more pickets and higher material cost; larger gaps reduce cost but let more light through.

For a privacy fence, gaps are often 0.5 to 1 inch. For a decorative or pool fence, gaps may be 2 to 4 inches. Check local building codes for maximum allowable gaps, especially for pool safety fences – many require gaps no wider than 4 inches.

Common Mistakes and How to Avoid Them

• Forgetting to convert units: Mixing feet and inches without converting is the most frequent error. Always work in inches for the formula.
• Rounding down instead of up: You cannot have a fraction of a picket, so always round up. Rounding down leaves a gap at the end.
• Ignoring the end posts: The formula counts pickets between posts. If you want pickets on the posts themselves, add one per post.
• Assuming the gap stays exact: When the total doesn’t divide evenly, the gap must be adjusted. The calculator gives you the adjusted gap automatically.

Limits of the Formula

This formula assumes a straight, level fence run. It does not account for corners, gates, or sloped terrain where pickets may need to be cut at angles. For a corner, you typically stop the picket run at the post and start fresh on the next side. For gates, you measure the gate opening separately and subtract it from the total run.

The formula also assumes uniform picket width and gap. If you plan to use pickets of varying widths, you’ll need to calculate each section separately. The result is a material estimate – always buy 5–10% extra to cover cutting waste and defects.

Frequently Asked Questions

How do I calculate pickets for a fence with a gate?

Measure the fence length excluding the gate opening. Calculate the pickets for that length, then add the pickets you plan to install on the gate itself. The gate frame is usually built separately, so the picket count for the gate is simply the gate width divided by the picket spacing.

What is the standard gap between fence pickets?

There is no universal standard – it depends on the fence purpose. Privacy fences often use 0.5 to 1 inch gaps, while decorative fences may use 2 to 4 inches. For pool safety, many codes require gaps no wider than 4 inches, and some require 2.375 inches (the width of a 2×4). Check your local code.

Should I round up or down when I get a decimal number of pickets?

Always round up. You cannot install a fractional picket, and rounding down will leave an unsightly gap at the end. The calculator rounds up automatically and then adjusts the gap to fit the exact length.

Does the gap include the picket width?

No. The gap is the open space between two adjacent pickets. The total spacing from the center of one picket to the center of the next is the picket width plus the gap.

How much extra should I buy for waste?

Add 5–10% to the calculated number to cover cuts, warped boards, and installation mistakes. For a fence with many corners or angles, use 10–15%.

Can I use this calculator for wood, vinyl, or metal pickets?

Yes, the formula only depends on the width and gap, not the material. Just enter the actual width of the pickets you plan to use.

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in len | Fence length | ft | 100 | 0
in pw | Picket width | in | 5.5 | 0
in gap | Desired gap | in | 2 | 0
out count | Number of pickets | - | ceil(len * 12 / (pw + gap)) | 0
out actual_gap | Actual gap | in | (len * 12 - count * pw) / (count - 1) | 2
out total_pickets | Total pickets incl. posts | - | ceil(len * 12 / (pw + gap)) + 1 | 0