Total Concrete Needed
0 m³
Including wastage allowance
Calculate concrete needed for fence post holes and installations
Professional concrete calculations for fence posts, including post hole dimensions, concrete volume, and material requirements for timber, colorbond, and brick fence installations across Australia in 2026.
Calculate concrete requirements for secure fence post installations
Accurately calculate concrete needed for fence post holes based on post size, hole dimensions, and fence height. Our calculator determines volume per hole and total concrete required for your entire fence project, accounting for standard post spacing in Australian installations.
Determine correct post hole depth based on fence height, soil conditions, and Australian building standards. Standard rule: bury 1/3 of post length plus 100mm for 1.2-1.8m fences, or minimum 600mm depth. Calculator provides recommendations for secure, long-lasting fence installations.
Support for timber paling fences, colorbond steel fences, picket fences, pool fencing, and brick-pier fences common in Australian residential and commercial properties during 2026. Calculate concrete for standard 90mm, 100mm, or 125mm posts with appropriate hole sizing.
Enter your fence specifications to calculate concrete requirements
Proper concrete installation is critical for fence stability, longevity, and structural integrity in Australian conditions during 2026. Post holes must be adequately sized and filled with appropriate concrete mix to resist wind loads, prevent post movement, and withstand ground movement from moisture changes in reactive clay soils common across Australia. Insufficient concrete or improper installation leads to leaning fences, loose posts, and premature fence failure requiring costly repairs.
The general rule for post depth is burying 1/3 of the total post length, with minimum 600mm depth for standard 1.8m high fences. Higher fences, exposed locations, or poor soil conditions require deeper holes up to 900-1200mm. Post holes should be 2-3 times the post width diameter to provide adequate concrete collar around the post. For 100mm timber posts, typical hole diameter is 250-300mm, creating concrete thickness of 75-100mm around all sides of the post.
Proper fence post installation requires digging holes to adequate depth (typically 600-900mm below ground), placing the post centrally, and filling around it with concrete. The post extends above ground to fence height, with panels attached on either side. Concrete must fully surround the post with 75-100mm thickness on all sides. Post depth should be 1/3 of total post length minimum, ensuring stability against wind loads and ground movement in Australian conditions.
Post Size: 90-100mm × 90-100mm treated pine
Post Spacing: 2.4 metres centres
Hole Depth: 600-750mm
Hole Diameter: 250-300mm
Concrete per Post: 30-50 litres
Most common residential fence in Australia 2026
Post Size: 50mm × 50mm or 75mm × 75mm steel
Post Spacing: 2.4-3.0 metres
Hole Depth: 600-750mm
Hole Diameter: 200-250mm
Concrete per Post: 20-40 litres
Popular low-maintenance option
Post Size: 75mm × 75mm or 90mm × 90mm
Post Spacing: 1.8-2.4 metres
Hole Depth: 500-600mm
Hole Diameter: 200-250mm
Concrete per Post: 20-30 litres
Decorative front yard fencing
Post Size: 50mm × 50mm aluminium or glass spigots
Post Spacing: 1.2-1.8 metres
Hole Depth: 600-750mm (compliance requirement)
Hole Diameter: 200-250mm
Concrete per Post: 25-40 litres
Must meet Australian pool fencing standards AS 1926.1
For cylindrical post holes. Diameter and depth in millimeters, result in litres. Multiply by number of posts for total volume. Add 10-15% wastage.
For 20m fence with 2.4m spacing = 9 posts × 53L = 477 litres = 0.48 m³ + 10% wastage = 0.53 m³ total
Calculate number of posts by dividing fence length by post spacing, then adding 1 for the final end post. For example, 20 metre fence with 2.4 metre spacing: 20 ÷ 2.4 = 8.33, round up to 9 posts total. This assumes posts at both ends. For fence joining existing structures at both ends, subtract 1 post if existing posts are reused. Corner posts and gate posts count as regular posts for concrete calculation purposes, though gate posts sometimes use slightly larger holes for additional stability.
Australian building practice recommends post depth equal to 1/3 of total post length as minimum, with 600mm absolute minimum for fences up to 1.8m height. Higher fences require proportionally deeper holes: 2.1m fences need 750-900mm depth, 2.4m fences require 900-1000mm depth. Exposed locations with high wind loads, sandy or soft soils, or fences supporting heavy gates need 150-300mm additional depth beyond standard guidelines. Hard clay soils may allow slightly shallower holes but not less than 600mm for any residential fence application.
| Concrete Type | Cost per 20kg Bag | Coverage | Advantages |
|---|---|---|---|
| Pre-Mixed Concrete | $8-$12 | 9-10 litres per 20kg bag | Just add water, consistent quality, easy for DIY |
| Rapid Set Concrete | $12-$16 | 9 litres per 20kg bag | Sets in 10-20 minutes, install posts same day |
| Post Mix Concrete | $10-$14 | 9-10 litres per 20kg bag | Specific for posts, good drainage, fast setting |
| General Purpose Concrete | $7-$10 | 10 litres per 20kg bag | Economical for large projects, standard strength |
| Manual Mix (Bags) | $9-$13 cement + sand/aggregate |
~15L per 20kg cement (in mix) | Cheapest for large jobs, custom strength |
| Ready-Mix Truck | $200-$280 per m³ | 1000 litres per m³ | Best for 20+ posts, professional quality |
Small Fence (10 metres, 5 posts): 250 litres concrete = 25-30 bags pre-mix at $8-12 per bag = $200-360 materials. DIY labour free, or $150-250 contractor labour = $350-610 total installed cost for post concrete only.
Standard Fence (20 metres, 9 posts): 480 litres concrete = 48-55 bags pre-mix = $384-660 materials. DIY saves labour, contractor charges $300-450 = $684-1,110 total for concrete installation.
Large Fence (40 metres, 17 posts): 900 litres = 0.9 m³ concrete. Consider ready-mix truck at $250-280 per m³ plus small load fee $80-120 = $330-400 total materials, more economical than 90+ bags. Contractor labour $600-900 = $930-1,300 installed.
Ready-Mix vs Bags: Break-even point typically 15-20 posts (0.7-0.9 m³). Above this volume, ready-mix truck is cheaper and faster. Below this, bagged concrete more practical despite higher unit cost.
While most residential boundary fences don't require building permits or formal engineering design in Australia during 2026, pool fencing must comply with AS 1926.1: Swimming Pool Safety - Fencing for Private Swimming Pools. This standard mandates minimum 1200mm height, specific post spacing requirements, and strength testing for barriers. Post holes for pool fences typically require 600-750mm minimum depth with adequate concrete for structural integrity to prevent barrier breaches.
Retaining wall fences or fences on steep slopes may require engineering design and compliance with local council requirements. High fences (over 2.1m) in some councils need permits and structural certification. Wind loading calculations per AS 1170.2 apply for exposed coastal locations or cyclone-prone regions in northern Australia. Consult local council requirements before commencing work on non-standard fence installations during 2026.
Concrete requirement depends on hole size and number of posts. Typical 300mm diameter × 750mm deep hole requires approximately 50 litres (5 × 20kg pre-mix bags) per post. For standard 20 metre fence with 9 posts at 2.4m spacing, you need 450 litres (45-50 bags) plus 10% wastage = 500 litres total (50-55 bags). Larger holes or deeper installations require more concrete per post. Use calculator above for your specific fence dimensions to get accurate material requirements.
Minimum 600mm depth for standard 1.8m high residential fences in Australia. General rule: bury 1/3 of total post length, so 1.8m fence requires 2.4m posts buried 600mm minimum. Recommended depths: 600-750mm for 1.8m fences, 750-900mm for 2.1m fences, 900-1000mm for 2.4m fences. Increase depth by 150-300mm for exposed locations, soft soils, or posts supporting gates. Pool fences require 600-750mm minimum for compliance with AS 1926.1 standard. Never less than 600mm for any residential fence application in Australian conditions.
Standard pre-mixed concrete sets enough to remove braces after 24 hours, reaches working strength in 3-7 days, and full strength in 28 days. You can install fence panels after 24-48 hours once concrete is hard. Rapid-set concrete sets in 10-20 minutes, allowing same-day panel installation after 4 hours minimum. Cold weather slows curing (add 50% time below 10°C), hot weather speeds it up. Don't load posts heavily or install gates until minimum 48 hours cure time. Humid conditions or rain during curing can weaken concrete - protect with plastic sheeting if rain threatens within 24 hours of pouring.
Normal pre-mixed concrete is fine for most DIY fence projects and costs $8-12 per 20kg bag. It allows longer working time (45-60 minutes) for positioning posts accurately. Rapid-set concrete ($12-16 per bag) is best when you want to complete fence same day, for repair of single posts in existing fence, or in cold weather when normal concrete cures slowly. Trade-off: rapid-set costs 30-40% more and you must work quickly (10-20 minute working time). For large projects with many posts, normal concrete is more economical and less stressful. For 1-3 posts or urgent repairs, rapid-set convenience justifies extra cost.
Not recommended for permanent fences in Australia. Dirt-set posts (backfilling with compacted soil only) work for temporary fences or very short garden fences under 1m height in sheltered locations. However, they're much less stable than concrete, allow post movement and rot, and fail quickly in wind or reactive clay soils common across Australia. Proper concrete installation costs $40-60 per post for materials but lasts 15-30+ years. Dirt-set posts often fail within 2-5 years requiring replacement. For any fence over 1.2m height, boundary fences, or exposed locations, concrete is mandatory for structural adequacy and longevity.
Calculate by dividing fence length by post spacing, then add 1. For example: 20m fence ÷ 2.4m spacing = 8.33, round up to 9 posts total (includes both end posts). Standard spacing: 2.4m for timber paling fences, 2.4-3.0m for colorbond, 1.8-2.4m for picket fences, 1.2-1.8m for pool fencing. Closer spacing provides stronger fence but costs more. Gates require posts on both sides (2 posts per gate). Corner posts count as regular posts. If fence connects to existing structure at one end and uses existing post, subtract 1 from total. Always order 1-2 extra posts for contingency or errors.
Post holes should be 2-3 times the post width in diameter. Standard sizes: 250-300mm diameter for 90-100mm timber posts, 200-250mm for 50-75mm steel posts, 300-350mm for 125mm heavy timber posts. Depth: minimum 600mm, recommend 750mm for 1.8m fences. Larger holes provide more concrete thickness around post (minimum 75mm all sides) for better stability and strength. Avoid oversized holes (over 3× post width) as they waste concrete unnecessarily. In rocky or hard clay, slightly narrower holes (2× post width) are acceptable if achieving required depth. Use post hole digger or power auger for clean vertical holes.
Break-even point is approximately 0.7-0.9 m³ (15-20 posts). Bagged pre-mix costs $800-1,100 per m³ equivalent when accounting for $8-12 per 20kg bag yielding 9-10 litres. Ready-mix truck delivers concrete at $200-280 per m³ but has minimum order 0.5-1.0 m³ plus small load fee $80-120. For small projects under 15 posts (0.7 m³), bags are more practical despite higher cost. For projects over 20 posts (0.9 m³), ready-mix truck saves $300-600 and is much faster. Manual mixing from cement bags cheapest option for very large projects but requires significant labour and skill to achieve consistent quality.
Official source for AS 1926.1 Pool Fencing standards and AS 3600 Concrete Structures guidelines used in fence post installation and structural concrete work across Australia.
Access Standards →Technical resources on concrete mixing, curing, and application for residential and commercial construction including fence post installations and small concrete works.
Explore CIA Resources →Industry standards, best practices, and construction guidelines for fence installation, concrete work, and residential building projects in Australian conditions during 2026.
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