Fence Calculator

Why fencing projects go over budget — and how to plan them properly

A fence looks like a straightforward project: measure the boundary, buy panels, dig some holes, and put it up. In practice, most first-time fence builders find themselves short by 2 or 3 panels, 1 bag of concrete, and a Saturday afternoon, because the arithmetic of fence building has more moving parts than it first appears. Posts are spaced along a run that rarely divides evenly into panel widths. Corners and gateposts eat into the panel count. And the concrete calculation — how many bags per post — is surprisingly easy to underestimate.

Getting it right the first time saves money, saves trips to the hardware store, and prevents the slightly awkward situation of running out of material with one section left to finish. A fence calculator handles all of that arithmetic in one pass. It divides the fence length into panels, counts the posts, calculates the rails, and works out the concrete volume per post based on the hole dimensions. The result is a complete material list and an honest cost estimate before you pick up a shovel.

Below we'll cover the standard fence dimensions, the post spacing rules, the concrete maths, and the cost ranges that give you a realistic budget for a DIY or professional installation.

How the fence calculator works

Ten inputs drive the total project:

• Unit — metres or feet for all dimensions.
• Total fence length — the full run along the boundary.
• Panel width — the width of one panel (typically 1.8 m or 6 ft).
• Post spacing — distance between post centres (typically 1.8–2.4 m).
• Waste buffer — extra material for cuts and offcuts.
• Hole depth and diameter — for the concrete estimate.
• Cost per panel, post, and concrete bag — for the material cost.
• Labour cost — the installation cost if you're hiring.

The calculations:

• Length with waste = length × (1 + waste ÷ 100).
• Panels = ceil(length with waste ÷ panel width).
• Posts = ceil(length ÷ post spacing) + 1.
• Rails = panels × 3 (standard 3-rail fence).
• Concrete volume per post = π × (diameter ÷ 2)² × depth.
• Concrete bags = ceil(total volume ÷ bag yield).
• Materials cost = panels × panel cost + posts × post cost + bags × bag cost.
• Total cost = materials + labour.
• Cost per unit = total ÷ length.

Everything runs in your browser. No address, boundary, or cost data is ever uploaded or stored.

A worked example: 30 m boundary fence

Consider a 30 m boundary fence with 1.8 m panels, 2 m post spacing, 60 cm deep holes at 25 cm diameter, and 10% waste.

• Length with waste: 30 × 1.10 = 33.0 m
• Panels: 33 ÷ 1.8 = 18.33 → 19 panels
• Posts: (30 ÷ 2) + 1 = 16 posts
• Rails: 19 × 3 = 57 rails
• Concrete volume per post: π × (0.125)² × 0.6 = 0.0295 m³ (29.5 L)
• Total concrete: 16 × 29.5 = 472 L
• Bags (at ~20 L per 20 kg bag): 472 ÷ 20 = 23.6 → 24 bags

At $45 per panel, $15 per post, $7 per bag of concrete, and no labour cost, the total is 19 × $45 + 16 × $15 + 24 × $7 = $1,263 — roughly $42 per metre of fence.

If a contractor quotes $80 per metre to install the same fence, the labour component alone is around $1,137. That's the trade-off most homeowners are weighing when they decide whether to build it themselves.

Standard fence dimensions

The table below shows typical dimensions for common fence types. These are the inputs most calculators expect:

Post height typically extends 60–90 cm above the fence for a cap, or is flush with the top of the top rail. Post diameter is usually 10–15 cm (4–6 in) for a residential fence.

Post spacing and depth rules

Two rules govern a fence that will stand straight for decades:

• Spacing: posts every 1.8–2.4 m. Tighter spacing (1.8 m) is standard for privacy fences with solid panels; wider spacing (2.4–3 m) is fine for lighter fences or where panels are rigid.
• Depth: the rule of thumb is one-third of the post's total length below ground. A 2.4 m post sits 80 cm deep; a 1.8 m post sits 60 cm deep.

In cold climates, posts must go below the frost line — sometimes 90 cm or more. If they don't, freeze-thaw cycles push them out of alignment over a few winters.

The hole is typically 3× the post diameter — a 10 cm post sits in a 25–30 cm hole.

Concrete per post: the maths

Concrete volume is a cylinder calculation:

• Volume = π × (radius)² × depth.
• For a 25 cm diameter, 60 cm deep hole: π × (0.125)² × 0.6 = 0.0295 m³ = 29.5 L.
• For a 30 cm diameter, 80 cm deep hole: π × (0.15)² × 0.8 = 0.0565 m³ = 56.5 L.

A typical 20 kg bag of concrete mix yields about 20 L when mixed. So the 25×60 cm hole takes 1.5 bags, and the 30×80 cm hole takes 3 bags.

Rules of thumb that save time:

• 1 bag per post for a 20 cm hole, 60 cm deep.
• 2 bags per post for a 25 cm hole, 60–70 cm deep.
• 3 bags per post for a 30 cm hole, 80 cm deep.

Always round up — running out of concrete halfway through a post is a bad time.

Fence cost per metre

Costs vary widely by material, height, and location. The table below is a rough benchmark for 2025–2026:

Urban properties with hard-to-reach boundaries and older properties with existing fences to remove sit at the higher end of every range.

Choosing fence materials

• Pressure-treated wood — the standard for residential privacy fences. Lasts 15–20 years with minimal maintenance.
• Cedar or redwood — naturally rot-resistant, beautiful grain, more expensive. Lasts 20–25 years.
• Vinyl / PVC — never needs painting, lasts 30+ years, expensive up front.
• Composite — wood-plastic blend, similar cost to vinyl, similar lifespan.
• Aluminium / steel — best for decorative or security fencing. Can last 50+ years.
• Chain-link — cheapest, least attractive, ideal for pet enclosures.
• Wrought iron — traditional, ornamental, very durable, expensive.

For most residential properties, pressure-treated wood is the value choice, cedar is the beauty choice, and vinyl is the low-maintenance choice.

Planning permission and boundary rules

Before you dig, check the local rules:

• Height limit — most jurisdictions allow fences up to 2 m (6.5 ft) in a backyard without permission. Front yards are often capped lower (1–1.2 m).
• Boundary ownership — you can only build on your side of the boundary line. The "good side" of a panel fence typically faces the neighbour.
• Right of access — your neighbour has the right to maintain their property. Don't block access to a shared wall or drainage.
• Corner visibility — some areas restrict fence height near road corners for traffic visibility.
• Listed buildings and conservation areas — often need explicit permission for any fence change.
• Homeowners' associations — HOA rules can be stricter than the law.

If you're unsure, a short call to your local planning department resolves almost everything.

Common fence-building mistakes

• Not measuring the full boundary. Including both sides of the property you're fencing.
• Forgetting corner posts. A corner needs its own post, not a shared one at the panel edge.
• Underestimating concrete. The most common material shortfall.
• Spacing posts by panel width alone. Posts should be evenly spaced along the run, and the last panel may need cutting.
• Skipping the frost line. Posts move within a season in cold climates.
• Not using pressure-treated wood below ground. Rot sets in within 3–5 years.
• Ignoring gate posts. Gates need stronger, thicker posts than fence panels.
• Forgetting the waste buffer. Always buy 5–10% more material than the calculation shows.

Frequently asked questions