How Much Concrete for a Single Fence Post
Setting fence posts in concrete is the most reliable method for creating sturdy, long-lasting fences. Whether you're building a new boundary fence or replacing damaged posts, understanding concrete requirements ensures you purchase the right amount of material without wastage.
Standard Fence Post Hole Dimensions
For a typical 90x90mm timber fence post, a hole diameter of 250mm provides adequate concrete around the post for solid anchoring. Depth should be approximately one-third of the total post length above ground, with 600mm being minimum for standard 1.8-metre fences. These proportions have been proven over decades of Australian fence building.
Concrete Volume Calculations
A 250mm diameter hole at 600mm depth contains approximately 0.029 cubic metres of space. Subtracting the post volume and adding wastage gives around 0.025 cubic metres of concrete per post, or roughly 2-3 bags of 20kg quick-set post mix. This accounts for the irregular hole shape typical of manual digging.
Quick-Set vs Standard Concrete
For fence posts, quick-set post mix is strongly recommended. Products like Rapid Set Post Mix set in 20-30 minutes, allowing you to continue with fence construction the same day. Standard concrete requires 24-48 hours before attaching rails, significantly slowing project progress.
Post Alignment During Setting
Quick-setting concrete leaves minimal time for adjustment. Set up string lines before mixing concrete and have a spirit level ready. Place the post, check alignment, add concrete around the post, recheck alignment, and hold or brace the post until initial set occurs. Working with a partner makes this process significantly easier.
Drainage Considerations
Water collecting around post bases accelerates timber decay. Place 50mm of gravel in the bottom of each hole before setting posts. Some builders also leave the concrete slightly below ground level and cap with gravel, allowing water to drain away rather than pooling against the timber.
Consistent Depth Technique
Use a depth gauge made from a stick marked at your target depth. Check each hole before setting posts to ensure consistent fence height. Digging all holes before setting any posts allows you to verify alignment and make adjustments before committing concrete.
Need Different Specifications?
Use our post hole calculator to enter your exact hole dimensions and post size. You can also explore our slab calculator or footing calculator for other concrete projects.