Fence Post Calculator
Plan posts for a straight run or a rectangular perimeter. Compute number of posts, spacing, or total run length — with gates/openings accounted for.
Calculation Steps
Practical Guide
Fence Post Calculator: Plan, Space, and Set Posts Correctly
A field-tested walkthrough that mirrors how you actually build a fence: confirm your run, account for corners and gates, choose spacing, size footings, and sanity-check concrete and post counts with worked examples.
Quick Start: From Property Line to Post Holes in Minutes
- 1 Measure or import your fence run(s). Include each straight segment and note corners and any gate openings you’ll leave clear.
- 2 In the calculator above, enter total length (or segment lengths), choose post spacing, and add gates with their widths. The tool will exclude gate spans when it calculates posts.
- 3 Select footing size (hole diameter and depth) and your preferred bag size or concrete unit. The calculator outputs hole volume and estimated bags per post, plus a total.
- 4 Review the post count along with “end/corner” logic. If your fence returns to the start, account for that shared corner only once.
- 5 Export or copy results and mark out the site with stakes or spray paint before digging.
Choosing Your Layout Method
There are two dominant ways to lay out posts. Your calculator supports both — pick the one that matches your fence kit or jobsite constraints.
Uniform Spacing (Center-to-Center)
Best when you’re stick-building on site and want consistent rhythm along the run.
- Pros: clean sightlines; easy to compute; flexible around gates.
- Cons: may leave a remainder bay at the end; requires custom rail cuts.
Micro-formula: \(N = \left\lfloor \frac{L’}{S} \right\rfloor + 1\), where \(L’ = L – \sum G_i\) and \(S\) is chosen spacing.
Panel-Based Layout (Fixed Panel Width)
Ideal if you’re using factory panels (e.g., wood or metal sections at fixed widths).
- Pros: fast installation; fewer cuts; predictable fastener layout.
- Cons: leftover gap likely unless you trim a panel; tight tolerance at corners.
Micro-formula: \(N = \left\lceil \frac{L’}{W_p} \right\rceil + 1\), where \(W_p\) is panel width and \(L’\) excludes gates.
Corner logic: Corners act like posts that support two runs. When computing total posts around a closed perimeter, avoid double-counting a corner post that serves both ends.
What Moves the Number: Spacing, Footings, Gates, and Soil
These levers change your post count and concrete needs the most.
Variables & Symbols
| Symbol | Meaning | Units |
|---|---|---|
| \(L\) | Total fence length (sum of straight segments) | ft or m |
| \(G_i\) | Gate \(i\) width | ft or m |
| \(L’\) | Effective length excluding gates \((L’ = L – \sum G_i)\) | ft or m |
| \(S\) | Chosen spacing (center-to-center) | ft or m |
| \(N\) | Number of posts (by method) | count |
| \(D\) | Hole diameter | in or mm |
| \(h\) | Hole depth | in or mm |
| \(V\) | Concrete volume per hole | ft³ or m³ |
Footing Volume (for concrete estimate)
Assuming a cylindrical hole, the per-post volume is:
\[ V = \pi \left(\frac{D}{2}\right)^2 h \] Convert \(D\) and \(h\) to the same units before calculating. If you enter inches, the calculator converts to feet/meters internally before summing totals.
Worked Examples
Two realistic scenarios show how the calculator handles spacing, gates, and footings. The math below mirrors the tool’s logic.
Example A (US units): Straight run with a gate
Inputs: fence length \(L\), one gate of width \(G_1\), spacing \(S\), footing \(D \times h\).
- 1 Effective length: \(L’ = L – G_1\).
- 2 Posts by uniform spacing: \(N = \left\lfloor \dfrac{L’}{S} \right\rfloor + 1\). If a terminal post is needed at the other end, add it.
- 3 Concrete per hole: \(V = \pi (D/2)^2 h\) (convert inches to feet before multiplying).
- 4 Total concrete: \(V_\text{total} = N \cdot V\).
Rounding: Post count is an integer. Volume is typically rounded up to the next full bag or practical purchase unit.
Example B (Metric): L-shaped fence with two gates
Inputs: segments \(L_1\) and \(L_2\), gates \(G_1\) and \(G_2\), spacing \(S\), footing \(D \times h\) in mm.
- 1 For each leg, compute \(L’_k = L_k – \sum G_{i,k}\) and posts \(N_k = \left\lfloor \dfrac{L’_k}{S} \right\rfloor + 1\).
- 2 If the inside corner is a shared post, subtract one to avoid double-counting.
- 3 Convert \(D\) and \(h\) to meters (e.g., mm ÷ 1000). Per-hole volume: \(V = \pi (D/2)^2 h\) in m³.
- 4 Total posts \(N = \sum N_k\). Total concrete \(V_\text{total} = N \cdot V\).
Check: Use the calculator’s segment mode to enter each leg separately and toggle the corner sharing option if provided.
Common Layouts & Footings
Use this reference to anticipate how layout choices affect counts and concrete.
| Layout / Condition | What Changes | Impact on Posts | Impact on Concrete |
|---|---|---|---|
| Straight run with uniform spacing | Even cadence; one remainder bay likely | Baseline \(N\) by \(S\) | Baseline \(V_\text{total} = N \cdot V\) |
| Panel-based system | Fixed panel width governs centers | \(\lceil L’/W_p \rceil + 1\) | Similar per hole; total scales with \(N\) |
| Multiple gates | Gate spans removed; add hinge/latch posts | Posts increase by gate posts; runs shrink | Total may rise or fall depending on gates |
| Corners & returns | Shared posts at corners | Avoid double count at the shared corner | Corner posts may use larger footings |
| Weak soil / higher wind | Deeper and/or wider footings | Post count unchanged | Higher \(V\) per post → more total concrete |
- Do: Keep all inputs in one unit system and convert before computing.
- Don’t: Mix inches and feet (or mm and m) in the same formula without conversion.
Buying, Logistics & Practicalities
Selecting Posts & Hardware
- Match post material and section to fence height and wind exposure.
- Use heavier or braced posts at corners, ends, and gate locations.
- Confirm fastener and bracket systems if using prefab panels.
Excavation & Concrete
- Mark centers from a control point; dry-fit gate spacing before digging.
- Excavate consistent diameters; bell bottoms only if allowed and practical.
- Consolidate concrete around posts and slope the top away from the post for drainage.
Sanity Checks & Codes
- Respect property lines, utilities, and HOA/municipal rules.
- Footing depth should meet local frost-line requirements.
- Confirm any additional requirements for pool barriers or privacy fences.
FAQs
How does the calculator count posts when I add gates?
The tool subtracts the gate widths from the total run and adds the required gate posts (typically one hinge and one latch post per gate). Gate spans aren’t included in the spacing math.
Do corners count as one post or two?
A true 90° corner is a single post serving both directions. When you close a perimeter, avoid double-counting that shared corner. The calculator’s corner logic mirrors this.
What spacing should I use?
Choose spacing based on fence type, height, and stiffness requirements. Smaller spacing increases rigidity and reduces rail deflection but uses more posts and concrete.
How deep should I dig the post hole?
Depth is governed by frost line and soil conditions. Use the calculator to test scenarios with deeper or wider footings; always follow local code requirements.
How do I estimate concrete bags from volume?
Enter your hole diameter and depth to compute volume per hole; then choose a bag size in the calculator to convert volume to bags. Round up for waste and spillage.
Can I mix feet/inches or meters/millimeters?
Keep a single system for input, then convert. Mixing units without converting is the most common source of mistakes in post counts and concrete totals.
What if my last bay is a different width?
It’s normal to have a remainder. You can absorb it at the last bay, distribute small adjustments across a few bays, or trim a panel (for panel-based systems).