The calculation, without hidden assumptions
Bag count should come from actual hole geometry and the yield printed on the concrete bag. MAXScanner calculates the cylindrical volume for each hole, applies the project allowance you choose and then rounds upward using your entered cubic-foot yield per bag.
How to use this calculator
Enter hole diameter and depth in inches and the number of holes.
Enter the cubic-foot yield shown on the concrete bag or supplier data; do not rely on a hidden bag-size assumption.
Add a project allowance if appropriate and an optional bag price to see the rounded material subtotal.
Where people use it
- •Fence and sign posts
- •Small deck or pergola posts where bagged concrete is specified
- •Comparing hole size or bag-yield scenarios
Example: ten 12 in × 36 in holes
A 12 in diameter, 36 in deep cylindrical hole is about 2.356 cubic feet. Ten identical holes are about 23.56 cubic feet before waste; the final bag count depends on the yield printed on the bag.
What the result does not assume
- •Real holes are rarely perfect cylinders, and posts or forms can displace concrete. Enter an allowance that matches the field condition and specification.
- •Foundation size and depth are structural/site decisions. This calculator does not choose them.
Frequently asked questions
Why do I enter bag yield instead of bag weight?+
Different mixes and package weights produce different volumes. Yield in cubic feet is the value needed to convert project volume to bags.
Does the post itself reduce concrete volume?+
This simple cylindrical estimate does not subtract post displacement. For large posts or precise work, account for displacement separately.
Does the result round to full bags?+
Yes. The adjusted concrete volume is divided by your entered bag yield and rounded up.
Semantic next steps
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Keep the result connected to the real job
MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.