Wood Fence Picket Calculator: Count & Spacing

This calculator works out how many wood fence pickets you need for a straight fence run and the exact gap between them. You enter the total fence length, picket width, and desired gap (or picket spacing), and it returns the number of pickets required plus the precise on-center spacing. It also shows the total linear feet of picket material so you can order accurately.

Formula

The core formula is simple: convert the fence length to inches, then divide by the sum of one picket width plus one gap. The result is the number of pickets needed, rounded up to the next whole number because you can’t buy a fraction of a picket.

Number of pickets = ⌈ (Fence length in inches) ÷ (Picket width + Gap) ⌉

Where:

• Fence length – total horizontal distance of the fence run, in feet (or convert to inches).
• Picket width – the actual width of one picket, in inches. Common sizes are 3.5, 5.5, and 7.5 inches.
• Gap – the space between adjacent pickets, in inches. This is the same as the “spacing” if you measure from the edge of one picket to the edge of the next.

The on-center spacing (the distance from the center of one picket to the center of the next) is simply picket width plus gap. That’s the number you use when marking rails.

Worked Example

Using the default values: fence length = 100 ft, picket width = 5.5 in, gap = 0.5 in.

1. Convert fence length to inches: 100 ft × 12 = 1200 in.
2. Add picket width and gap: 5.5 + 0.5 = 6.0 in (this is the on-center spacing).
3. Divide total inches by spacing: 1200 ÷ 6.0 = 200 pickets.
4. Since 200 is already a whole number, no rounding up is needed.
5. Total picket material: 200 × 5.5 in = 1100 in = 91.67 ft.

The calculator shows 200 pickets, 6.00 in on-center spacing, and 91.67 ft of picket material.

When to Use This Calculator

Use this tool when you’re planning a new wood privacy fence, a decorative picket fence, or even a screen wall. It’s also handy when you need to replace a section of an existing fence and want to match the spacing exactly. The calculator works for any straight run; for corners or gates, calculate each section separately and add extra pickets for the gate frame if needed.

For a privacy fence, you typically set pickets with no gap (0 in) or a very small gap (0.25 in) to block views. For a decorative or airy fence, gaps of 1–3 inches are common. The calculator lets you try different gaps to see how the count changes.

How to Choose Picket Width and Gap

Your choice affects both look and cost. Here are typical scenarios:

• Privacy fence: 5.5-in pickets with 0–0.5-in gap. This uses more wood and creates a solid barrier.
• Picket fence (dog-ear or flat top): 3.5-in or 5.5-in pickets with 1–3-in gap. Looks airy and lets light through.
• Board-on-board: Two layers of pickets, each layer offset. The calculator gives the count per layer; you’ll double it.

Also consider the style of picket: dog-ear, Gothic, scalloped, or square. Width is the same regardless of style, but the top shape doesn’t affect spacing.

Common Mistakes and How to Avoid Them

One frequent error is mixing units: fence length in feet but picket width in inches. Always convert everything to inches before dividing. Another is forgetting to round up – even if the math gives 199.2 pickets, you need 200. Also, the on-center spacing is not the gap; it’s the gap plus the picket width. When you mark the rail, you measure from the center of one picket to the center of the next, not from edge to edge.

Another mistake is ignoring the end posts. The calculator assumes the pickets start and end at the fence ends. If you have corner posts or gate posts, you may need to trim the first or last picket to fit, which could add one extra picket to your order. Always buy 5–10% extra for waste, cuts, and mistakes.

Limitations of the Formula

This formula assumes the pickets are evenly spaced and the fence length is a straight line. It does not account for:

• Posts that interrupt the run – you’ll need to calculate each section between posts separately.
• Angled or curved fences – the formula works for straight segments only.
• Picket overlap (board-on-board) – you need double the count.
• Trim pieces at the ends – you may need to cut a picket narrower to fit.

For a fence with posts, measure the distance between the inside faces of the posts for each section. That’s the length to enter. For a gate, you’ll need pickets for the gate frame, which is usually a separate calculation.

Cost and Material Estimation

Once you have the picket count, you can estimate material cost by multiplying by the price per picket at your local lumber yard. Picket prices vary by wood type (cedar, pine, composite) and quality. Also add the cost of rails (usually 2×4s), posts, concrete, and nails or screws. A typical 100-ft fence with 5.5-in pickets and 0.5-in gaps uses about 200 pickets, which is roughly 92 linear feet of picket material – but you’ll also need about 200 ft of rails (two rails per section) and 10–12 posts. Always get a detailed quote from a supplier.

Frequently Asked Questions

How many pickets do I need for a 100 ft fence with 5.5 inch pickets and 0.5 inch gap?
Using the formula: 100 ft × 12 = 1200 in, divided by (5.5 + 0.5) = 6.0 in, gives 200 pickets exactly. If the gap were 1 inch, you’d need 1200 ÷ 6.5 = 184.6, so 185 pickets.

What is the difference between on-center spacing and gap?
On-center spacing is the distance from the center of one picket to the center of the next. It equals picket width plus gap. The gap is just the empty space between two pickets. When marking rails, use on-center spacing.

Should I round up the number of pickets?
Yes, always round up to the nearest whole number. You can’t buy a fraction of a picket, and you’ll likely need to cut some for corners or ends. It’s also wise to add 5–10% extra for waste.

Does the calculator work for board-on-board fences?
No, because board-on-board uses two overlapping layers. Calculate the count for one layer using the formula, then double it. The gap is typically 0 because the boards overlap.

How do I measure the fence length for a section with posts?
Measure the distance between the inside faces of the two end posts. That gives the clear span for pickets. If you measure from outside to outside, you’ll be off by the width of the posts.

Can I use this for metal or vinyl pickets?
Yes, the math is the same for any material. Just enter the actual width of the picket and the desired gap. The calculator works for wood, composite, vinyl, or metal.

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in length | Fence length | ft | 100 | 0
in pwidth | Picket width | in | 5.5 | 0
in gap | Gap between pickets | in | 0.5 | 0
out count | Number of pickets | pickets | ceil(length * 12 / (pwidth + gap)) | 0
out oc | On-center spacing | in | (pwidth + gap) | 2
out total_ft | Total picket material | ft | ceil(length * 12 / (pwidth + gap)) * pwidth / 12 | 2