For repeated fence or support holes of the same size. Concrete occupies the hole volume left after subtracting the embedded post.
- Hole shape and depth
- Choose round or rectangular; enter the hole diameter or both sides, then the full vertical depth from the top of the hole to its base.
- Post section
- Choose none, round or rectangular. The model subtracts that section through the full hole depth.
- Quantity and extra
- Identical holes are multiplied before your allowance is added.
Hole and post shapes are independent. The post must fit inside the hole; a rectangular post in a round hole is checked by its diagonal.
- Excavation and total displaced volume; net concrete per hole and across all holes.
- Added allowance and total concrete required.
Ten round holes with round posts embedded through the entire modelled depth.
| Quantity | Value |
|---|---|
| Hole diameter; post diameter | 0.30 m; 0.10 m |
| Depth; quantity; extra | 0.60 m; 10; 10 % |
| Excavation; displacement | 0.424; 0.047 m³ |
| Net; required | 0.377; 0.415 m³ |
Net = π/4 × (hole diameter² − post diameter²) × depth × quantity. Extra is applied after subtraction.
Ready-mix planning uses the required volume and a truck capacity you enter. Bagged mix uses the finished yield of one bag; bag weight alone does not determine it. Whole bags and loads round up. Optional cost uses your price per volume or per bag.
Bag-count example for a separate slab: 0.660 m³ divided by an assumed yield of 0.020 m³ per bag gives 33 bags. This yield is an example input, not a specification for every 40 kg or 50 kg bag. Check the selected product.
Metric and imperial entry are supported. In these examples, lengths are converted to metres before multiplication; displayed volumes are rounded to three decimals. The arithmetic retains the unrounded value.
The extra percentage is a chosen allowance for this estimate. It is not a required building-code value. Geometry estimates quantity; it does not select concrete strength, foundation depth or reinforcement.
The model does not have a separate post embedment depth or a bell-shaped base. If the post stops above the bottom, account for that solid concrete region separately.
Why is excavation larger than concrete?
The post occupies part of the hole. No-post mode keeps that part as concrete.
Does it choose a safe foundation depth?
No. Enter the depth specified for the actual soil, loads and design.
- Why is excavation larger than concrete?
- The post occupies part of the hole. No-post mode keeps that part as concrete.
- Does it choose a safe foundation depth?
- No. Enter the depth specified for the actual soil, loads and design.
Measurements, units and material terms
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