How this calculator works
Each hole is a cylinder or rectangular prism with constant cross-section. Multiply its plan area by depth and repeated quantity. Reverse modes use the total net volume before waste, while the concrete order adds a separate allowance. The full hole is assumed filled: posts and other inserts must be deducted separately. Irregular excavation, tapered sides and bell footings need their own measured volumes.
Formula
Circular V = pi x diameter^2 x depth x quantity / 4; rectangular V = length x width x depth x quantity; depth = total V / (area x quantity); order = V x (1 + allowance).
Worked example
Three holes 1 m in diameter and 2 m deep contain 4.71239 m3 in total. A rectangular 2 x 3 m hole containing 12 m3 is 2 m deep; with 10% allowance, full-hole concrete is 13.2 m3.
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Frequently asked questions
Do I deduct a fence post?
Yes, if it occupies part of the filled space. This tool reports full-hole capacity; subtract the embedded post volume before ordering.
Is excavation spoil the same volume?
No. Removed soil often expands. The result is in-place geometric volume, without a soil bulking factor.
Can hole quantity be fractional?
A reverse calculation reports exact volume equivalents. For an actual job, use an integer count and recalculate the concrete order.