Gravel layer at bottom
Concrete collar only
What This Fence Post Concrete Calculator Is For
This Fence Post Concrete Calculator helps DIY builders, homeowners, and contractors estimate how much concrete is required for fence posts accurately.
It is designed for common fencing projects where users need quick, reliable answers for concrete volume and concrete bag quantities — without complex engineering calculations.
This calculator is commonly used for:
- Concrete volume calculation for fence posts
- Round and square fence post holes
- Estimating concrete per post and total concrete
- Concrete bag estimates (25 kg, 40 kg, 60 lb, 80 lb)
- Optional gravel layer at the bottom of post holes
- Optional concrete collar (partial pour)
- Ready-mix concrete cost estimates
- Metric and imperial units
- DIY and small construction projects
What Is a Fence Post Concrete Foundation?
A fence post concrete foundation is a concrete-filled hole that secures a fence post in the ground and transfers loads into the soil.
Concrete around fence posts helps:
- Prevent post movement and rotation
- Improve fence durability
- Resist frost heave and soil movement
- Extend the service life of the fence
Fence post foundations are typically poured directly into excavated holes, either fully filled with concrete or partially filled using a concrete collar.
How to Calculate Concrete for Fence Posts
To calculate concrete correctly for fence posts, you need to know the hole size, hole depth, number of posts, and expected waste.
This calculator uses true geometric volume formulas instead of rough guesses or “bags per hole” rules of thumb.
Required inputs include:
- Number of fence posts (manual or calculated)
- Hole shape (round or square)
- Hole diameter or width
- Hole depth
Optional inputs include:
- Fence length and post spacing (automatic post count)
- Gravel thickness at the bottom of the hole
- Concrete collar height (partial pour)
- Waste percentage
All values can be adjusted, and results update instantly.
Manual Post Count vs Fence Length Calculation
This calculator allows two different ways to define the number of fence posts.
Manual post count is best if you already know how many posts you will install.
Fence length calculation is useful when planning a new fence layout. By entering fence length and post spacing, the calculator estimates the required number of posts automatically.
Optional corner and end posts can also be included for more accurate planning.
Round vs Square Fence Post Holes
This calculator supports both common fence post hole shapes.
Round holes are the most common and are typically drilled or dug using post hole diggers or augers.
Square holes are sometimes used for larger posts or when holes are formed manually.
The calculator automatically applies the correct volume formula for each hole shape.
Gravel Layer Under Fence Posts
A gravel layer at the bottom of the hole improves drainage and reduces moisture buildup around the post.
Typical gravel thickness ranges from:
- 50–150 mm (2–6 inches)
If enabled, the calculator subtracts the gravel thickness from the concrete fill depth and estimates gravel volume separately.
Concrete Collar for Fence Posts
Instead of filling the entire hole with concrete, some builders use a concrete collar around the top of the post.
A concrete collar:
- Uses less concrete
- Allows better drainage below
- Is common for light-duty fencing
If enabled, this calculator pours concrete only in the upper portion of the hole based on the specified collar height.
How Much Waste Should I Add?
A waste factor helps prevent running out of concrete due to irregular holes, soil collapse, or material loss during pouring.
Typical waste values:
- 0–5% – clean holes and careful pouring
- 5–10% – standard residential fence work
- 10–15% – loose soil or uneven excavation
You can set waste to 0% if you want an exact theoretical volume.
Common Mistakes When Estimating Concrete for Fence Posts
- Forgetting to include waste
- Using incorrect hole depth
- Mixing metric and imperial units
- Underestimating concrete bag quantities
- Ignoring gravel thickness
- Buying too little concrete
Using a calculator helps avoid delays and additional trips to the supplier.
Fence Post Concrete vs Other Foundation Types
Fence post foundations are simple, isolated concrete supports designed for vertical elements only.
Compared to other foundation types:
- Fence post foundations use less concrete than slabs
- They require minimal excavation
- They are faster and cheaper to install
For larger structures or posts carrying higher loads, consider pad footings or pile foundations.
FAQ
How deep should fence post holes be?
Fence post holes are commonly 600–900 mm (24–36 inches) deep, depending on soil conditions, post height, and local frost depth.
How much concrete do I need per fence post?
Concrete per post depends on hole diameter, depth, gravel thickness, and whether a full pour or concrete collar is used. This calculator provides both per-post and total values.
Can I use this calculator for gate posts?
Yes. Gate posts typically require deeper or wider holes. Adjust hole dimensions accordingly for accurate results.
Does this calculator include gravel?
Yes. If enabled, the calculator estimates gravel volume separately and reduces the concrete volume accordingly.
Is the concrete cost estimate accurate?
No. The cost estimate is a rough approximation only. Concrete prices vary by region, supplier, and delivery conditions.
Planning a Fence or Outdoor Structure?
CraftFrame plans include post layouts, spacing guidance, foundation recommendations, and step-by-step instructions to help you build correctly and efficiently.
For isolated concrete pads under posts, use our Pad Footing Calculator.
For drilled or deep foundations, use our Pile Concrete Calculator.
For slab-on-grade foundations, use our Concrete Slab Calculator.