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Work out exactly how much concrete — or how many bags of postcrete — you need to set your fence posts.
It depends on the hole size, not the post. As a rule of thumb, set a post to about a third of its above-ground height in the ground (so a 1.8m fence needs roughly a 600mm hole), in a hole two to three times the width of the post. This calculator works out the hole volume, subtracts the post, adds a 10% allowance for spillage and uneven holes, and converts it to ready-mix volume or 20kg postcrete bags.
| Hole (dia × depth) | Post | Concrete per post | 20kg bags |
|---|---|---|---|
| 200mm × 600mm | 75mm | ~16 litres | ~2 bags |
| 250mm × 600mm | 100mm | ~24 litres | ~3 bags |
| 300mm × 750mm | 100mm | ~46 litres | ~5 bags |
Figures are approximate and rounded up — holes are rarely perfectly regular. A 20kg bag of postcrete sets roughly 0.011 m³; always allow a little extra.
• Big run or a base to go with it? Full concrete calculator
• See our volumetric concrete (mixed on site, pay for what you use)
• Back to all concrete calculators
For a handful of posts, bagged postcrete is quick and convenient (it sets in minutes). For a long fence line or a commercial run — roughly 20+ posts — the bags add up fast, and ready-mix or volumetric concrete delivered to site usually works out cheaper and faster. This calculator gives you both so you can compare.
A common rule is to bury about a third of the post’s above-ground height — so a 1.8m high fence needs a hole around 600mm deep, and taller or exposed fences need more. The hole is usually dug two to three times the width of the post. Your ground conditions and fence height set the final depth.
For a typical 250mm × 600mm hole around a 100mm post, roughly 3 bags. Bigger or deeper holes need more — the calculator works out the exact number for your hole size.
Yes — we supply ready-mix and volumetric concrete across Greater Manchester and Cheshire, ideal for large fencing runs where bags aren’t practical. Tell us the number of posts and hole size and we’ll quote the volume.
Calculator uses hole volume (round or square) minus the post, plus a 10% allowance; bag estimate based on a 20kg postcrete bag setting ~0.011 m³. A guide only — confirm quantities for your job.