Pile foundation calculator
Concrete for bored piles and the grillage beam that ties them together.
Fill in the fields and the result will appear here automatically.
Adds equal cylindrical pile volumes and a rectangular grillage volume, then includes your chosen concrete allowance. Diameter and depth are entered in metres. This is a geometric budget, not foundation design: pile count, bearing capacity, soil, loads and reinforcement are not determined. Overlapping volumes are not automatically subtracted.
How it works
Formula and logic
One pile V₁=πD²h/4; piles Vp=n·V₁; grillage Vg=L·B·H. Net V=Vp+Vg, total V·(1+w/100), allowance V·w/100. n is a positive safe integer; D and h are positive, grillage dimensions nonnegative, all numbers finite. A zero in any grillage dimension gives Vg=0; w is 0–50%.
Example
Twelve 300 mm piles 1.8 m deep with a 32 m grillage need 6.979 m³ of concrete. Grillage width and height are 0.4 m, allowance 5%, with no overlapping volumes.
Fields and units
- Number of piles — unitless
- Pile diameter — m
- Pile depth — m
- Grillage length — m
- Grillage width — m
- Grillage height — m
- Allowance — %
How to use
- — Enter how many piles the plan has, and their diameter and depth.
- — Enter the grillage beam dimensions, or zeros if there is none.
- — Add an allowance for what is lost in delivery and pouring.
- — Compare pile and grillage volumes separately; cost and load capacity are not calculated.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- Geometric volume only; foundation capacity and design suitability are not checked.
FAQ
Why is the grillage bigger than the piles?
It is not a general rule: the ratio depends on dimensions. In the example, 12 piles with D=0.3 m and h=1.8 m give 1.527 m³; a 32×0.4×0.4 m grillage gives 5.12 m³. Other dimensions change the ratio.
What if I have no grillage?
Set at least one grillage dimension to zero. Its volume becomes zero; this is an input convention, not a conclusion that a foundation without grillage is appropriate.
Does depth mean the whole pile or the part in the ground?
Whatever you will pour. If the pile stands proud of the ground, include that part — it takes concrete too.
Is the reinforcement included?
No. Pile cages and grillage bars depend on the design and are a separate count.
Why not just use the strip foundation calculator?
Because a strip is one continuous trench of concrete, while this is discrete columns plus a beam on top. The two parts are counted separately here, and their ratio is the useful part.