Free Calculator · By SubcontractorHub Editorial Team · Published November 2026
Fence Post Concrete Calculator for the Hole Around the Post
A fence post concrete calculator on this page is the hole minus the post. A 10 inch hole, 24 inches deep, with a 3.5 by 3.5 inch post and no gravel, is 0.921 cubic feet. Bags wait for a yield you type.
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Book a DemoHow the Fence Post Concrete Calculator Subtracts the Post
Cylinder, then the wood, then the count.
10 inches, 24 inches, and a 3.5 inch post are the numbers in the boxes. They are not a code depth. Bags stay blank until you type a yield.
One hole is 0.921 cubic feet after the post. That post total 0.921 cubic feet, or 0.034 cubic yards. No bag count, because no yield was typed.
All calculations are estimates based on historical information and should be verified by the user.
Important: the yield is typed
All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.
This Fence Post Concrete Calculator Is Not a Tube Form
A round cardboard form is the sonotube calculator. That page does not subtract a post, and it does not assume a dug hole. A spread footing with a different shape is the concrete footing calculator. Volume in yards for a slab or a pile of aggregate is the cubic yard calculator.
How many pickets the fence needs is the fence picket calculator. A price for the whole run, which this page does not print, is the fence cost calculator. Concrete in the hole is a quantity. The bid is a different sheet.
Worked hole
Diameter 10 inches. Depth 24 inches. Gravel 0. Post 3.5 inches by 3.5 inches, which is the dressed size people often mean by a 4×4. One post is 0.921 cubic feet, or 0.034 cubic yards. Multiply by the post count. This page will not invent an 80 pound yield.
| Line | Formula | Example |
|---|---|---|
| Hole | π × radius² × depth | 1.091 cu ft |
| Post | width × thickness × depth | 0.170 cu ft |
| Concrete | hole − post | 0.921 cu ft |
| Bags | only if a yield is typed | blank |
How should you order the concrete?
- Hole diameter of the auger you will use, in inches.
- Hole depth from grade to the bottom, in inches. This page does not set a frost line.
- Gravel thickness, if any. That depth is not concrete.
- Actual post width and thickness. A nominal 4×4 is often 3.5 inches.
- Post count, including gates if those holes match.
- Cubic feet per bag from the bag, or order in cubic yards. No price.
What the Hole Volume Will Not Decide
Public search for this kind of calculator returned other volume tools. Several printed bag counts from a yield this page did not fetch, so those bag counts are not copied. If the sack lists cubic feet, type it. If it does not, stay in cubic yards and let the supplier convert.
A round steel post is not a rectangle. Leave the post boxes at the size of the section that actually displaces concrete, or set them to zero and order the full hole, which is the safer overage. Hollow posts and brackets can use less mix. Follow the anchor sheet.
No structural spacing, no wind load, and no setback are on this page. Those belong with the local rule and the fence manufacturer, not in a cylinder.
Frequently Asked Questions
How does the fence post concrete calculator get cubic feet?
It treats the hole as a cylinder and subtracts the post. A 10 inch hole, 24 inches deep, with a 3.5 by 3.5 inch post and no gravel, is about 0.921 cubic feet for one post. Bags appear only if you type cubic feet per bag.
Does gravel count as concrete?
No. Inches of gravel at the bottom are removed from the concrete depth. This page does not turn that gravel into a bag count.
Is this the same as a sonotube calculator?
No. A sonotube calculator measures a round tube form. This page measures a dug hole with a post standing in it. A spread footing is a different tool.
Does the page pick a hole depth?
No. Frost depth, wind, and fence height are not on this page. Type the hole you will dig. No code depth was fetched.
Measure the Hole, Then Price the Bag Elsewhere
Cubic feet are the hole. Dollars are the supplier.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.