Fence material calculator

What a fence material calculator does

A fence material calculator turns fence run lengths into a material list: the number of bays or panels, posts, rails and pickets. Enter each run and its gate width, the maximum bay width between posts, the rails per bay and your picket width and gap, and it returns totals with a waste allowance and a per-run breakdown.

The core rule is simple: a straight run needs one more post than it has bays. A 40 ft run with posts no more than 8 ft apart has 5 bays and 6 posts. Rails follow the bays (two rails per bay gives 10 rails), and pickets follow the length of fence divided by the picket width plus the gap.

The tool handles several runs at once and one centered gate per run. It treats each run independently, so a corner post shared by two runs is counted in both unless you enter it under shared corner posts. It also estimates post-hole concrete, gate hardware and the step per bay on sloping ground. The bay width you enter is your choice, not a structural recommendation, and the tool does not check wind loads, post depth, property lines or permit rules.

How to use the fence material calculator

1. Choose Imperial or Metric, then choose the Infill: Palings for individual pickets or boards, or Panels for prefabricated fence panels. The tool uses paling for what US suppliers call a picket.
2. Set the Maximum bay width, the post spacing you will not exceed (8 ft is common for wood fences), and the Rails per bay.
3. For picket fences, enter the Paling width (the actual picket width, such as 3.5 or 5.5 in) and the Paling gap. Enter the number of Shared corner posts where two runs meet so each is counted once.
4. Set the Ground: Level, Stepped panels on a slope or Racked infill on a slope, with the Ground grade in percent. Enter the Post hole diameter and Post hole depth, pick a Premix bag preset (or a custom yield) for the footings, set the Hinges per gate and a Waste allowance percentage.
5. In the run table, enter a name, Run length and Centred gate width for each straight run. Use Add run for each side of the yard, and leave the gate at 0 where there is none.
6. Read the bays, posts before and after shared corners, rails, pickets or panels, post-hole concrete and bags, gate hinges and latches, the slope step per bay and the per-run table. Download the PDF or CSV, copy the result, or use Save inputs to reopen the layout later.

Worked example

Imperial: A 40 ft run with no gate and 8 ft bays needs five bays and six posts. With two rails per bay, it needs ten rails.

Metric: A 12 m run with no gate and 2.4 m bays needs five bays and six posts. With two rails per bay, it needs ten rails.

How many fence posts do I need?

For one straight run, posts = bays + 1, and bays = run length ÷ maximum bay width, rounded up. Rounding up keeps every bay at or under your maximum spacing, so when a run doesn't divide evenly the bays end up slightly shorter than the maximum.

A gate adds posts. The calculator splits a run with a centered gate into two equal sides, counts the bays on each side separately and adds an end post to each side, so both gate posts are included. A 40 ft run with a 4 ft gate has two 18 ft sides of 3 bays each: 6 bays and 8 posts, against 5 bays and 6 posts without the gate.

Corners are where estimates drift. If three runs meet at two corners, the tool counts each corner post once in each run. Enter 2 under shared corner posts and the tool subtracts them from the total.

How many pickets per 8 ft fence section?

Pickets = length ÷ (picket width + gap), rounded up. The gap is added once to the length, so a run that starts and ends with a picket is not overcounted. Wood pickets are commonly about 3-1/2 in or 5-1/2 in wide (sold as 1x4 and 1x6). Measure yours, because widths vary by mill and product.

A privacy fence with no gap needs the most pickets, and wood shrinks as it dries, so tight-butted pickets usually open small gaps over time. Board-on-board fences are two overlapping spaced layers; run the calculator once for each layer with its own width and gap, and add the results.

Per-bay counts in the table are for a single 8 ft bay, rounded up. On long runs the calculator rounds once per run side, so the total is closer to the per-foot figure.

Worked example: a backyard fence with a gate

A backyard has a 60 ft rear fence and two 90 ft side fences, with a 4 ft gate centered in the right side. The fence uses 8 ft maximum bays, 5-1/2 in pickets with a 1/2 in gap, two rails per bay and 10% waste. Entered as three runs, the calculator returns 32 bays, 36 posts and 476 pickets before waste. The right side is split into two 43 ft sides of 6 bays each, which is why it has one more post than the left side.

• Rails: 32 bays × 2 = 64 rails, or 96 with three rails per bay.
• Pickets with 10% waste: 476 × 1.1 = 523.6, rounded up to 524.
• Posts after the corner deduction: the rear fence shares a corner post with each side, so the real count is 36 − 2 = 34 posts.
• Counted at the values you enter: post-hole concrete from the hole diameter and depth, premix bags at the preset yield, and hinges and a latch per gate. Not included: the gate leaf, post caps and fasteners. Use the concrete calculator for any other footings.

Post spacing, rails and post depth

Wood picket and privacy fences are commonly built with posts at 6 to 8 ft centers, with two rails on lower fences and three rails on 6 ft privacy fences. Prefabricated wood, vinyl and metal panels come in fixed widths, so set the bay width to the post-center spacing in the manufacturer's instructions rather than the nominal panel width.

A common rule of thumb is to set posts about one-third of their length into the ground, and below the frost line where local practice requires it. That is a starting point, not a design: tall fences, exposed sites and solid infill catch more wind, and your building department may set its own requirements.

For posts set in concrete, the concrete per hole is the hole volume minus the post. A 10 in diameter hole 30 in deep around a 4x4 post (3-1/2 in actual) holds about 1.15 ft³, roughly two 80 lb bags of premixed concrete at a typical yield of 0.6 ft³ per bag. Check the yield printed on the bag you buy.

Who it is for and when to use it

Method, formulas & assumptions

For each run, gate width is deducted from infill. Bays = ceil(infill length ÷ maximum bay width). An internal gate splits the infill evenly into two sides, each rounded independently; posts include gate boundaries. Net posts = posts − shared corners. Post-hole concrete = π(hole ⌀ ÷ 2)² × depth × net posts. Stepped slopes drop bay width × sin(atan(grade)) per bay.

Imperial inputs are converted with exact factors (1 ft = 0.3048 m, 1 lb = 0.45359237 kg, 1 US gal = 3.785411784 L) before the calculation runs in SI, then results are converted back.

Common mistakes to avoid

• Counting posts as length ÷ spacing. A straight run always needs one more post than it has bays, plus the extra posts a gate creates.
• Double-counting corner posts. The tool treats runs independently, so enter one shared corner post for each corner where two runs meet.
• Using nominal picket sizes. A 1x6 picket is about 5-1/2 in wide; entering 6 in undercounts by roughly one picket in twelve.
• Entering the panel's nominal width as the bay width. Use the post-center spacing from the panel manufacturer, which allows for the post and brackets.
• Forgetting the gate itself. The calculator deducts the gate opening from the infill and lists hinges and a latch per gate, but not the gate leaf.
• Building to a boundary you have not confirmed. Check the survey and the local height and setback rules before ordering.

Scope & limits

Runs are independent; enter the shared corner posts to deduct them. One centred internal gate per run, with the hinges you set and one latch each; other gate positions should be split into separate runs. Spacing, hole size and slope handling are user supplied, not a structural recommendation.

Frequently asked questions

Further reading

• Fence, gate and boundary template
• Residential setback requirements
• Building permit process explained
• All materials & quantities tools
• All free architecture & construction tools
• Harth resource library

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