Fence Post Calculator
Enter your total fence run and the spacing you plan to use, and this works out the post count, the concrete you need per hole and the material cost. Spacing, post material and soil type are what actually move the number.
Measure the full run, including every side. Posts are counted per span plus one extra to close the run.
Post count is spans plus one. A 30m run at 2.4m centres is 12.5 spans, which rounds up to 13 spans and therefore 14 posts, not 13. Corners and any change of direction each need their own post as well.
As a bagged concrete guide, a standard 300mm diameter by 600mm deep hole takes roughly two to three 20kg bags per post once you subtract the volume of the post itself. Deeper or wider holes climb quickly, so a 900mm clay footing can be four bags.
💰 Ways to save
- Measure and set out the run before you order anything. Walk the line with a string and mark every post position, because the real spacing is almost never the nominal one once you account for corners, a gate opening and a run that does not divide evenly. Setting out first tells you the true post count and often saves a full extra post per side, plus the trip back to the yard for the two extra bags you did not allow for.
- Buy concrete in bulk bags rather than handy 20kg packs if you have more than about ten holes. Bagged rapid set is convenient and priced accordingly, and the premium over standard bagged mix is around 30 to 50 percent per hole. Standard mix is fine for line posts as long as you can brace them overnight, so save the rapid set for gate posts and corners where you genuinely want to work the next morning.
- Do not buy the same post section for the whole fence. Line posts carry sheeting load only, while corners, ends and gate posts carry tension and swing load, so a sensible build uses a lighter and cheaper line post with a heavier section at the four or five points that actually need it. Specifying the heavy post everywhere can add several hundred dollars to a suburban boundary for no structural benefit.
- Check whether the fence is a shared boundary before you commit. Under the dividing fence legislation in every state and territory, a neighbour can be liable for half the cost of a sufficient dividing fence, but only if you serve the correct written notice before the work starts. Doing the job first and asking afterwards usually means you wear the entire bill.
How we estimate this
## How many fence posts you actually need
Pricing reviewed: June 2026.
Pricing reviewed June 2026. Indicative Australian costs, not a quote.
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Understanding fence posts in Australia
How many fence posts you actually need
The arithmetic is simple but the mistake is common. Divide the total run by your chosen post spacing to get the number of spans, round up to the next whole number, then add one post to close the run. A 30 metre boundary at 2.4 metre centres gives 12.5 spans, which rounds to 13 spans and therefore 14 posts. Every corner and every change of direction needs its own post, and every gate needs two, so a rectangular backyard fenced on three sides with one gate will typically carry three or four more posts than a straight line calculation suggests. The calculator above starts from your run length and spacing and applies that plus one rule, but it is worth walking the line with a string and marking each position before you order, because a run that does not divide evenly usually forces one shortened final span.
What post spacing is right for your fence
Spacing is not a free choice, it is set by what the fence carries. Colorbond and steel sheeted fencing is normally specified at a maximum 2.4 metre span, and most manufacturers treat anything wider as outside the installation instructions, which puts the sheeting warranty at risk and lets the rails visibly bow within the first year. Timber paling fencing runs at the same 2.4 metres for a standard 1.8 metre high fence, tightening to about 1.8 metre centres on exposed or windy sites, on sloping ground, or where the fence is 2.1 metres or higher and therefore catching much more wind. Rural wire and post and rail fencing is the exception and comfortably runs at 3 metres or more, because the fabric is porous and the wind load is a fraction of a solid panel.
Post material and what each costs in 2026
Treated pine posts to H4 durability class are the cheapest option, typically $18 to $32 each for a 2.4 metre 100 by 100 section, and they are the standard behind most timber paling fences. Galvanised steel line posts for Colorbond systems run roughly $28 to $50 each depending on section and colour, and the matching heavier corner, end and gate posts are $60 to $130. Hardwood posts sit at $45 to $90 and are chosen for exposed post and rail or for a fence where the post is a visible feature. Structural galvanised posts for wide gates or retaining duty are $110 to $250 each. Across a 30 metre suburban boundary the material difference between a pine build and a hardwood one is often $600 or more, which is why most people mix sections rather than specifying the dearest post along the whole run.
Concrete per post, and how deep to dig
The working rule for a domestic fence is to bury a third of the total post length, which means a 1.8 metre high fence uses a 2.4 metre post with 600mm in the ground. A hole of 300mm diameter by 600mm deep is about 42 litres of volume, and once you subtract the post itself you are looking at roughly two to three 20kg bags of premixed concrete per post. At $9 to $14 a bag in 2026 that is $20 to $40 of concrete per hole before you add anything else. Bulk bags and yard mix work out substantially cheaper once you pass about ten holes, and rapid set mix carries a 30 to 50 percent premium that is worth paying only on gate posts and corners where you want to load the fence the following day.
Why soil type changes the footing
Soil is the variable people underestimate. Reactive clay, which is widespread through Adelaide, western Melbourne, western Sydney and much of south east Queensland, swells when it is wet and shrinks back in a dry spell, and that cyclic movement will lever a shallow footing loose within a few seasons. In reactive ground the footing should go to at least 750mm and often 900mm, and belling the base of the hole slightly wider than the top gives the concrete a shoulder so it cannot be drawn straight up. Sandy and loose fill has the opposite problem, offering almost no lateral grip, so the answer is a wider hole rather than a deeper one. Rock and shale do not need a deep footing at all, but they add hire cost, because a hand auger will not touch them and you will be paying for a rock auger or a jackhammer for the day.
Concrete method, bracing and cure time
There are two accepted methods. Wet mixing in a barrow and pouring gives the strongest and most predictable result and is what a professional fencer will do. Dry pouring, where you tip the bagged mix straight into the hole and add water on top, is faster and is widely used on light domestic fences, but it relies on the water reaching the full depth of the hole and is unreliable in clay that sheds water. Whichever you use, crown the top of the concrete slightly above ground level and slope it away from the post so water sheds rather than pooling against the timber or the galvanising, because ponding at the collar is the single most common cause of premature post failure. Brace every post plumb and leave standard mix at least 48 hours, and a full seven days before you hang a gate.
Budgeting the whole job, not just the posts
Posts and concrete are usually about a third of a fence budget. The rest is the rails, sheeting or palings, fixings, and labour if you are not doing it yourself, and installed fencing in 2026 commonly lands between $85 and $180 per metre for Colorbond and $90 to $200 for timber paling depending on height and site access. Use the estimate above to price the post and footing component accurately, then treat it as a line in the larger fence budget rather than the whole picture. If the fence sits on a shared boundary, serve your neighbour the written fencing notice required in your state before work begins, since that notice is what creates their liability for half of a sufficient dividing fence.
Frequently asked questions
How many fence posts do I need for a 30 metre fence?
At the standard 2.4 metre spacing, 30 metres is 12.5 spans, which rounds up to 13 spans and therefore 14 posts. Add one post for every corner or change of direction and two for each gate opening, so a typical three sided backyard with one gate usually needs three or four more posts than the straight line figure.
How deep should fence posts be set in Australia?
The working rule is to bury a third of the total post length, so a 1.8 metre high fence uses a 2.4 metre post with 600mm in the ground. In reactive clay take the hole to 750mm or 900mm and bell the base slightly wider than the top, because clay movement will otherwise lever a shallow footing loose within a few seasons.
How many bags of concrete per fence post?
A standard 300mm by 600mm hole works out to roughly two to three 20kg bags once you subtract the post volume, or about $20 to $40 per hole at 2026 bagged prices of $9 to $14. A 900mm deep clay footing can take four bags, and bulk mix becomes cheaper than bags once you are past about ten holes.
Can I space fence posts 3 metres apart?
Only for wire, post and rail, or light rural fencing where the fabric lets wind through. Colorbond and timber paling systems are specified to a maximum 2.4 metre span, and going wider both voids the sheeting warranty and lets the rails sag noticeably within the first year.
What does a fence post cost in 2026?
Treated pine H4 posts run about $18 to $32 each, galvanised or Colorbond steel line posts $28 to $50, hardwood $45 to $90, and heavy structural gate or corner posts $110 to $250. Most builds mix a cheaper line post with a heavier section only at corners, ends and gates.
Do I have to tell my neighbour before replacing a boundary fence?
Yes, if you want them to contribute. Every state and territory has dividing fence legislation that makes a neighbour liable for half the cost of a sufficient dividing fence, but only when you serve the prescribed written notice before the work starts. Build first and you will normally wear the whole bill yourself.
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