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Post Hole Concrete Calculator

Post Hole Concrete Calculator estimates bagged concrete around posts for fence, mailbox, sign, and light post holes. Enter job dimensions in U.S. customary units, adjust supplier assumptions, and get purchase-ready quantities instantly.

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HOW IT WORKS

Formula and assumptions

Use π × (diameter ÷ 2)² × height × quantity, subtract post displacement where shown, divide cubic feet by 27, then apply waste.

Diameter is outside-to-outside and depth is the filled height.
Each cylinder uses the same dimensions.

FIELD CHECK

Before you order

Use the actual hole diameter and the actual post width or diameter; the calculator subtracts post displacement before waste.

Worked example

Example: with diameter 10 in, height / depth 30 in, number of cylinders 12, post shape Square, the post hole concrete calculator returns 0.56 cu yd for material to order. The supporting check is bags to buy: 26 bags. Replace the prefilled measurements and supplier assumptions with the project values before ordering.

PROJECT GUIDE

Using this calculator well

WHEN TO USE IT

Best use of this calculator

Use the result as a planning estimate, then verify field measurements and product-specific data before ordering or building.

INPUTS EXPLAINED

What each input means

Diameter: Enter the measured value and choose the matching unit (in, ft, cm, mm).
Height / depth: Enter the measured value and choose the matching unit (in, ft, cm, mm).
Number of cylinders: Enter the project value used by the calculation.
Post shape: Choose the option that matches the project: Square, Round, Do not subtract post.
Actual post width / diameter: Set the actual square width or round diameter; choose no subtraction for an empty form.
Waste allowance: Enter the project value in %.
Material density: Enter the project value in lb/cu ft.
Bag yield: Enter the project value in cu ft/bag.
Truck capacity: Enter the project value in cu yd.
Price per bag: Enter the project value in $.

COMMON MISTAKES

Checks that prevent bad estimates

Mixing units or entering a measurement in a different unit than the selected field unit.
Using a planning default when the exact manufacturer or supplier specification is available.
Rounding intermediate measurements too early instead of rounding the final purchase quantity.
Ignoring waste, compaction, cuts, laps, settlement, or full-package rounding where the project requires them.

SOURCES & REVIEW

How this estimate is supported

The implemented formula, assumptions, and worked example on this page are the calculator-specific reference. BuildYard's broader rules are documented in the Calculation Methodology and Sources & References.

For material density, coverage, yield, dimensions, package quantity, price, and other product-specific values, the current manufacturer or supplier specification should override a planning default.

Last reviewed: September 15, 2026, as part of the site-wide calculator workflow validation pass. See the BuildYard Changelog.

LEARN THE METHOD

Guides related to this calculator

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COMMON QUESTIONS

Post Hole Concrete Calculator FAQ

What does the Post Hole Concrete Calculator calculate?

It converts the measurements for fence, mailbox, sign, and light post holes into the buying units normally used for bagged concrete around posts, with the relevant waste, package, weight, or cost outputs shown on the result card.

How accurate is this post hole concrete calculator?

The geometry is calculated from the values you enter. Final ordering accuracy still depends on field measurements, supplier density or coverage, product dimensions, compaction, cuts, and the selected allowance.

What should I verify for fence, mailbox, sign, and light post holes?

Use the actual hole diameter and the actual post width or diameter; the calculator subtracts post displacement before waste. Confirm the selected product, field conditions, and purchasing increments before placing the order.

Should I round the result up?

Yes for indivisible buying units such as bags, sheets, bundles, pallets, boxes, bars, and truck loads. The calculator rounds those purchase quantities up automatically.

KEEP ESTIMATING

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