Post Hole & Footing Concrete Calculator
Specialized concrete takeoff
Add post holes and standalone footings
Result
Calculation summary
Enter values to see the result
Section preview
Hole, footing and post displacement
How to use this calculator
- 1Create one group for every distinct hole or footing geometry and enter its quantity and measurement unit.
- 2For post holes, select no post, a round post or a square post so embedded volume can be subtracted explicitly.
- 3Use the bell-bottom shape only when the project specifies the shaft diameter, enlarged base diameter and bell height.
- 4Enter waste and the exact mixed yield printed on the selected bag before reviewing bag count and optional cost.
Formula
Net concrete = excavation geometry − embedded-post displacement; order volume = net concrete × (1 + waste %)
Round shapes use cylinder volume, rectangular shapes use length × width × depth, and a bell bottom uses a shaft cylinder plus a conical-frustum base.
Calculation steps
- Convert every dimension to meters and calculate excavation volume per group.
- For bell bottoms, add the straight shaft above the bell to the conical-frustum volume.
- Subtract the entered round or square post volume only for post-hole shapes.
- Multiply by quantity, sum groups and apply waste.
- Divide by user-entered mixed bag yield and round up to whole bags.
- Multiply bag count by the entered price when cost is enabled.
Worked example
Four 12 in diameter × 36 in deep holes around 4 in square posts require about 0.229 m³ of net concrete. With 10% waste and 0.45 ft³ mixed yield per bag, the calculator rounds the order to 20 bags.
Assumptions
- Dimensions describe the concrete-filled geometry, not required footing design. Depth, diameter, frost protection, bearing area, reinforcement and uplift resistance must come from the project design.
- Hole walls are treated as ideal cylinders, rectangular prisms or a straight shaft plus conical frustum. Irregular excavation, collapse, groundwater and overbreak require field allowance.
- Post displacement assumes a constant cross-section through the entered concrete depth and ignores hardware, taper and voids.
- Bag yield is never inferred from bag weight; use the manufacturer-stated mixed yield for the exact product.
- The tool does not check soil bearing, frost depth, utilities, excavation safety, reinforcement, anchors, embedment durability or code compliance.
- Cost includes only entered bag price.
Sources
Frequently asked questions
Why subtract the post volume?
A post occupying part of a filled hole displaces concrete. The subtraction is optional and uses the entered constant post cross-section.
Can I calculate several hole sizes?
Yes. Add a separate group for every geometry and quantity.
Is bag weight enough to determine yield?
No. Products with the same bag weight can have different mixed yields, so enter the yield printed for the selected product.
Does it determine required hole depth?
No. Depth must come from the approved project design and local conditions.
What is the bell-bottom formula?
It combines the straight cylindrical shaft above the bell with a conical frustum transitioning from shaft radius to base radius.
When should ready-mix be considered?
Large orders may be more practical as ready-mix, but minimum order, access and placement decisions are local supplier questions.