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
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- 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.
Match each input label on the calculator to the real measurement, amount, rate, unit, or setting for your job.
The formula in plain language
In plain language: The calculator finds round hole volume, subtracts the round post volume inside the hole, multiplies the net fill by the number of holes, adds waste, converts to cubic yards, and rounds 60 lb and 80 lb bag counts up. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
The calculator finds the round hole volume, subtracts the round post volume, multiplies by the number of holes, adds waste, converts to cubic yards, and rounds bag counts up.
How to read the answer
Use the 80 lb bag count as the quick shopping number, then check cubic feet per hole if one hole looks too big or too small.
- 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.
- For example, six 12 inch by 30 inch holes with 4 inch posts and 10% waste need about 11.52 cubic feet, or 20 eighty-pound bags.
Common mistakes to avoid
The big mistakes are using the wrong hole depth, forgetting the post takes up space, and trusting the calculator to choose a safe depth for the job.
- 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.
- Do not treat dry-setting, wet-mixing, or fast-setting instructions as the same for every product. Check the bag or manufacturer guide.
Quick fence post example
Say you have six holes that are 12 inches wide and 30 inches deep. Each hole has a 4 inch post inside it, and you add 10% waste.
The calculator subtracts the post volume, so the total concrete is about 11.52 cubic feet. That is about 0.43 cubic yards, or 20 eighty-pound bags.
Why post volume matters
If you fill the whole hole as if the post was not there, the estimate is high. The post is already occupying part of the hole.
This matters more when you have many posts, larger posts, or deeper holes. It also helps when you are comparing bag counts before a store run.
What this does not decide
This page does not pick a safe hole depth or width. Fence height, gate size, deck loads, uplift, wind, soil, frost depth, drainage, and local code can all matter.
Use the approved plan, product instructions, or local professional guidance for the actual hole size. Use this calculator to estimate concrete after those dimensions are known.
Research and references
These references help check the measurements, units, limits, or safety notes used in this guide.
Worked examples for Post Hole Concrete Calculator
11.52 ft3 total, about 0.43 yd3, 20 eighty-pound bags
11.52 ft3 total, about 0.43 yd3, 20 eighty-pound bags
0.96 ft3, about 2 eighty-pound bags
9.24 ft3 total, about 16 eighty-pound bags
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 measurements, amounts, units, or options the page asks for.
What is the Post Hole Concrete Calculator doing with my inputs?
In plain language: The calculator finds round hole volume, subtracts the round post volume inside the hole, multiplies the net fill by the number of holes, adds waste, converts to cubic yards, and rounds 60 lb and 80 lb bag counts up. The examples on the page are there so you can compare your inputs with a worked example 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 depth filled with concrete in inches. Post diameter: the round-equivalent width of the post that takes up space inside the hole. Quantity: how many matching holes to estimate. Waste percent: extra concrete for uneven holes, overfill, spillage, and ordering cushion.
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, soil, drainage, bracing, product instructions, and local code can change what you actually need. Also check the unit, scale, mode, and result limit because small input changes can change the answer.
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.
What if my post is square?
Use the closest equivalent diameter for a rough estimate or calculate the square post area separately. For big jobs, a contractor takeoff is safer.
Related tools
- Fence CalculatorEstimate fence panels and posts from perimeter, panel width, post spacing, and gates.
- Concrete Column CalculatorEstimate concrete for round columns, piers, and tube forms.
- Concrete Footing CalculatorEstimate concrete volume and bag counts for straight rectangular footings.
- Concrete CalculatorEstimate slab volume, cubic yards, cubic meters, and common 40, 60, and 80 lb bag counts.
Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
- Home & ProjectsBrowse the full category for related tools that help with the same job.
- All free toolsSearch the complete Access Free Tools library by task, category, or tool name.
- All calculator and utility guidesFind more plain-language examples, formulas, mistakes, and result explanations.
- Free calculator resourcesStart here when you are not sure which calculator page fits.
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 save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.