Quick start
- Enter hole diameter and depth in inches.
- Enter the post diameter so the tool can subtract the space occupied by the post.
- Enter the number of matching holes and waste percent.
Best uses
These are the situations this tool is meant for. If your task is close to one of these, the examples and notes below can help you choose the right inputs.
- Estimate concrete bags for fence posts.
- Plan concrete for deck support holes.
- Subtract post volume from round hole volume.
- Compare hole sizes before buying concrete.
What this calculator is solving
The Post Hole Concrete Calculator estimates concrete around posts by using round hole volume and subtracting the post volume inside each hole.
You do not need to memorize the formula first. Start by matching each input label on the calculator to the number, date, unit, or setting you actually have.
The formula in plain language
In plain language: The calculator finds the round hole volume, subtracts the round post volume inside the hole, multiplies by the number of holes, adds waste, and rounds bag counts up. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
If that sounds abstract, use the example cards on the calculator page. They show a complete set of inputs and the kind of answer you should expect.
How to read the answer
Read the headline result first. Then look at the smaller supporting lines because they explain the parts behind the answer, such as totals, units, ranges, or formula steps.
- 80 lb bags is the main quick shopping number for many small projects.
- Cubic yards and cubic feet show the total adjusted concrete volume.
- Concrete per hole helps you spot an unusually large or small entry.
Common mistakes to avoid
If the answer looks strange, the most likely cause is a small input mismatch: the wrong unit, date, weight, scale, mode, or policy assumption.
- Do not make the post diameter larger than the hole diameter.
- Do not ignore frost depth, gate loads, deck loads, or fence manufacturer rules.
- Do not forget gravel bases or special footing shapes if your plan requires them.
Research and references
These references shaped the calculator assumptions, unit choices, or safety notes.
Examples from the calculator
About 20 eighty-pound bags
Post concrete estimate
Small bag estimate
FAQ in plain language
When should I use the Post Hole Concrete Calculator?
Use it when your task matches one of these common needs: Estimate concrete bags for fence posts. Plan concrete for deck support holes. It works best when you already know the values, dates, units, or settings the page asks for.
What is the Post Hole Concrete Calculator doing with my inputs?
In plain language: The calculator finds the round hole volume, subtracts the round post volume inside the hole, multiplies by the number of holes, adds waste, and rounds bag counts up. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
What do the main Post Hole Concrete Calculator inputs mean?
Hole diameter: the width across the round hole in inches. Hole depth: the filled depth in inches. Post diameter: the width of the post that takes up space inside the hole. Quantity: how many matching holes to estimate.
How should I read the Post Hole Concrete Calculator answer?
Read the headline estimate first, then check the material, waste, coverage, and unit lines. For project tools, the supporting lines are often the difference between a rough idea and a list you can actually shop from.
What should I double-check before trusting the answer?
Post depth, hole width, gravel base, frost depth, uplift, gate loads, deck loads, and local code can change what you actually need. Also check that you used the right unit, date, scale, or mode because small input changes can change the result.
Why does the calculator subtract the post volume?
The post occupies part of the hole, so concrete only fills the space around it. Subtracting the post keeps the estimate closer than treating the whole hole as concrete.
Related tools
- Fence Calculator Estimate fence panels and posts from perimeter, panel width, post spacing, and gates.
- Concrete Footing Calculator Estimate concrete volume and bag counts for straight rectangular footings.
- Concrete Calculator Estimate concrete volume for a slab in cubic feet, cubic yards, and bags.
Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to paste the expression and result into notes, homework, a message, or another document. Check the units and assumptions before copying.