Concrete Calculator
Setting fence posts in concrete? Get a more precise volume for each footing based on your actual hole diameter and depth.
Calculate Concrete NeededFence Calculator
Work out exactly how many posts, rails, and pickets or boards you need for your fence project. Pick a style, enter your fence length, height, post spacing, and any gates — the calculator instantly builds a materials estimate.
Number of Posts
— posts
Rails
—
Pickets
—
Fence style—
Total fence length—
Gate deductions—
Fence sections—
Concrete (post-set estimate)—
How this calculator works
The fence calculator starts from your total fence length, removes the space taken up by gates, then works out how many posts, rails, and pickets or boards fill in the rest.
1. Gate deductions — gate openings don't need fence sections, but do need their own posts:
Fenceable Length = Total Fence Length − (Gate Count × Gate Width)
2. Fence sections — the fenceable length divided by your post spacing, rounded up:
Sections = ⌈ Fenceable Length ÷ Post Spacing ⌉
3. Number of posts — one post at each end of every section, plus an extra post for each gate opening:
Posts = Sections + 1 + Gate Count
4. Rails — for privacy and picket styles, based on how many rails per section you set (we suggest 2–4 depending on fence height):
Total Rails = Rails per Section × Sections
5. Pickets or boards — for privacy/picket fences, pickets fill each section's width; for horizontal fences, boards stack to the fence's height instead:
Pickets per Section = ⌈ Post Spacing ÷ (Picket Width + Gap) ⌉
Boards per Section = ⌈ Fence Height ÷ (Board Width + Gap) ⌉
6. Waste allowance — extra rails and pickets/boards to cover cuts and mistakes (not applied to posts, since post count is fixed by the layout):
Final Quantity = ⌈ Raw Quantity × (1 + Waste % ÷ 100) ⌉
We also include a rough concrete estimate for setting posts, based on a configurable number of bags per post — adjust it to match your post size and hole depth.
Example calculation — using this calculator's default values: a 100 ft privacy fence, 6 ft tall, posts spaced every 8 ft, 1 gate that's 4 ft wide, 3 rails per section, 5.5 in pickets with no gap, and a 10% waste allowance:
Gate Deduction = 1 × 4 = 4 ft
Fenceable Length = 100 − 4 = 96 ft
Sections = ⌈96 ÷ 8⌉ = 12
Posts = 12 + 1 + 1 = 14
Total Rails = 3 × 12 = 36 → with 10% waste = ⌈36 × 1.10⌉ = 40
Pickets per Section = ⌈8 ÷ (5.5 ÷ 12)⌉ = ⌈17.45⌉ = 18
Total Pickets = 18 × 12 = 216 → with 10% waste = ⌈216 × 1.10⌉ = 238
Concrete Bags = 14 posts × 1 bag per post = 14 bags
With these inputs, the calculator recommends 14 posts, 40 rails, 238 pickets, and 14 bags of concrete — enough to frame and enclose the full 100 ft privacy fence run, including the extra post needed for the gate opening.
Factors That Affect Your Fence Estimate
Fence height
Height drives the auto-suggested rail count — this calculator recommends 2 rails up to 4 ft, 3 rails up to 6 ft, and 4 rails above that, since taller sections need more horizontal support. It also determines how many boards stack up on a horizontal-style fence.
Post spacing
Wider post spacing means fewer posts but each section spans a longer run, which can affect rail sag and how many pickets fit per section. Tighter spacing (6 ft) is common for taller or wind-exposed fences; wider spacing (8 ft) is typical for standard residential runs.
Gate count and width
Every gate removes its width from the fenceable run and adds one extra post to frame the opening. Getting gate count and width right matters — entering gates that don't exist, or the wrong width, will throw off both your post count and section count.
Fence style
Privacy and picket styles calculate rails plus pickets that fill each section's width; horizontal styles skip rails entirely and instead stack boards to the fence's height. Switching styles changes which materials — and which formula — the calculator uses.
Waste percentage
The waste allowance is applied to rails, pickets, and boards (not posts, since post count is fixed by the layout) to cover cut-offs, mismeasurements, and damaged pieces. A higher percentage is worth using for complex layouts with lots of corners or angle cuts.
Tips for a More Accurate Estimate
Order a few extra pickets or boards
Beyond the waste percentage already built into this estimate, it's worth keeping a handful of matching pickets or boards on hand for future repairs — replacing a single damaged picket years later with mismatched material or a discontinued profile can be difficult.
Round up your post count
Posts are sold as whole units, and this calculator already returns a whole number — but when you buy, round up to the next full or half bundle if your supplier sells posts in packs, so you're not short one post on installation day.
Check your local frost-line depth
The concrete bag estimate assumes a standard hole size — it doesn't know your local frost line. In colder climates, posts often need to be set below the frost line to prevent heaving, which usually means a deeper hole and more concrete per post than the default suggests.
Budget for gate hardware separately
This calculator accounts for the extra post and the length taken up by each gate opening, but not the gate panel, hinges, latch, or drop rod. Price those out separately based on the gate style and hardware finish you plan to use.
Limitations of This Estimate
This calculator assumes a straight, flat fence run measured as a single total length. It doesn't account for sloped or uneven terrain — on a hillside, fence sections are often stepped or raked to follow the grade, which can change post spacing and picket cutting in ways this tool can't calculate automatically.
It also doesn't include gate hardware (hinges, latches, drop rods, or the gate panel itself), fasteners, or post caps, and the concrete bag estimate assumes a standard footing size rather than your specific post diameter and hole depth. The suggested rail count is a general planning guideline, not a substitute for your local building code or wind-load requirements — always confirm rail count and post spacing with local code before building a fence that needs to meet a permit.
Frequently Asked Questions
Privacy fences use tightly-spaced vertical pickets with no gap. Picket fences use narrower vertical pickets with a visible gap between them. Horizontal fences use wide boards stacked flat to the fence height instead of vertical pickets, and are attached directly to posts without rails.
8 feet is a common default for wood fence posts, but spacing can range from 6–8 feet depending on your fence height, wind load, and local building code. Adjust it to match your plan.
A gate needs its own posts to hang from at both edges of the opening. This calculator assumes one of those posts is shared with the adjoining fence line and adds one extra post per gate to account for the other.
It's a rough planning number — actual concrete use depends on your post size, hole diameter, and hole depth. Use it as a starting point and confirm with your post size and local frost-line depth requirements.
Posts equal your number of fence sections plus one (for the final end post), plus one extra post per gate opening. This calculator works that out automatically from your total length, post spacing, and gate count.
The rail count field auto-fills based on your fence height — 2 rails for fences up to 4 ft, 3 rails up to 6 ft, and 4 rails for anything taller — but it's only a starting suggestion. Once you type a value into that field yourself, the calculator stops overriding it, even if you later change the height.
10% is a reasonable default for a straightforward run with few corners. Increase it for projects with many angle cuts, a fence line that isn't perfectly straight, or if you're less experienced with cutting lumber, since more material tends to end up as offcuts.
The default is 1 bag per post, but this varies with post size and hole depth — a wider post or a deeper hole (especially one dug below the frost line) needs more. Check your bag's yield in cubic feet against your hole's volume and adjust the "concrete bags per post" field accordingly.
A common rule of thumb is to set posts about one-third of their above-ground height into the ground, though many installers also dig deeper to get below the local frost line in cold climates. This calculator doesn't set a depth for you — check your local building code and frost-line depth before digging.
It will give you a rough materials estimate, but it assumes a flat, level run. On sloped ground, fences are often stepped or raked to follow the grade, which can change how pickets are cut and may affect post spacing — treat the result here as a starting point rather than a final count.
Add up the total straight-line length of every side you're fencing and enter that as your total fence length — this calculator treats the whole run as one continuous line. Keep in mind each corner needs its own post, so for a very irregular layout it can be more accurate to calculate each straight side separately and add the results together.
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