How Much Concrete for Fence Posts in Australia
Setting fence posts in concrete is one of the most common DIY concreting jobs in Australia. Getting the right amount of concrete ensures your fence stands strong for years, whether you're building a standard timber paling fence or a more substantial boundary fence.
Australian Fence Post Sizes
The most common timber fence post sizes in Australia are 90×90mm and 100×100mm for standard residential fencing. Steel posts, popular for their durability and termite resistance, typically come in 65×65mm sizes. For heavier-duty applications like front fences or dividing fences that need to support gates, 125×125mm timber posts provide extra strength.
Recommended Hole Dimensions
A good rule of thumb is to dig your post hole at least three times the width of the post. For a 100mm post, this means a hole diameter of 300mm. The depth should be approximately one-third of the total post length that will be above ground. For a standard 2.4 metre fence post where 1.8 metres is above ground, you would bury 600mm in concrete. Most Australian councils and fencing contractors recommend a minimum depth of 450mm for standard fences and 600mm for structural posts.
How the Calculation Works
This calculator determines the concrete volume by calculating the cylindrical volume of each hole and subtracting the volume occupied by the post itself. The formula uses π × radius² × depth for the hole volume, minus the post dimensions multiplied by the depth it extends into the concrete. This gives you an accurate figure for the actual concrete needed, not just the hole size.
Tips for Setting Posts in Concrete
Rapid-set concrete is ideal for fence posts because it sets quickly and eliminates the need for temporary bracing overnight. Some products, like Rapid Set Concrete Post Mix, can be poured dry into the hole around the post and simply watered. This makes the job much easier for DIYers working alone. For best results, place about 50mm of gravel at the bottom of each hole for drainage before adding concrete.
Council Regulations
Australian fencing regulations vary by state and local council. Boundary fences between neighbours are typically covered by state fencing acts, which specify height limits and cost-sharing arrangements. Front fences often have stricter height restrictions, usually limited to 1.2 metres without council approval. Corner properties may have visibility requirements that affect fence placement. Always check with your local council before building, especially for fences over 2 metres high or within certain distances of property boundaries.
Common Post Projects
Beyond standard fence posts, this calculator works for deck posts that need substantial footings, pergola posts that may require deeper embedment for structural stability, and letterbox posts. For structural applications like decks and pergolas, consider using larger posts and deeper holes than you might for a simple fence, and always check if your project requires engineering certification or a building permit.