How Many Bags of Concrete per Fence Post?
A 4x4 post in a hole 10 in wide with 2 ft 6 in of concrete takes 3 × 80 lb bags of the 80 lb size, or 4 × 50 lb bags of the 50 lb size, with the waste allowance added and the count rounded up once.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Count the bags for your own postsExample to try: Hole diameter 10 in, Hole depth 3 ft, Post side 3 1/2 in
Bags per post, by post, hole width and depth of concrete
Bags of concrete mix for one post, by post, hole diameter and depth of concrete, in three bag sizes, with the waste allowance added
| Post and hole | 2 ft deep, 50 lb | 2 ft deep, 60 lb | 2 ft deep, 80 lb | 2 ft 6 in deep, 50 lb | 2 ft 6 in deep, 60 lb | 2 ft 6 in deep, 80 lb |
|---|---|---|---|---|---|---|
| 4x4 post in a 8 in hole | 2 × 50 lb bags | 2 × 60 lb bags | 1 × 80 lb bag | 2 × 50 lb bags | 2 × 60 lb bags | 2 × 80 lb bags |
| 4x4 post in a 10 in hole | 3 × 50 lb bags | 3 × 60 lb bags | 2 × 80 lb bags | 4 × 50 lb bags | 3 × 60 lb bags | 3 × 80 lb bags |
| 4x4 post in a 12 in hole | 5 × 50 lb bags | 4 × 60 lb bags | 3 × 80 lb bags | 6 × 50 lb bags | 5 × 60 lb bags | 4 × 80 lb bags |
| Round post in a 8 in hole | 2 × 50 lb bags | 2 × 60 lb bags | 1 × 80 lb bag | 2 × 50 lb bags | 2 × 60 lb bags | 2 × 80 lb bags |
| Round post in a 10 in hole | 3 × 50 lb bags | 3 × 60 lb bags | 2 × 80 lb bags | 4 × 50 lb bags | 3 × 60 lb bags | 3 × 80 lb bags |
| Round post in a 12 in hole | 5 × 50 lb bags | 4 × 60 lb bags | 3 × 80 lb bags | 6 × 50 lb bags | 5 × 60 lb bags | 4 × 80 lb bags |
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
The depth is the concrete only; the gravel base under the post is a separate line in the calculator. The round size is a typed starting value, and a larger post is entered as its own measured side in the calculator: check your lumber's actual size. The bag yields come from QUIKRETE's published sheet. Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers.
What changes the count
The concrete is the hole's volume less the post's. A wider hole holds more: the same post in a hole 1 ft wide takes 4 × 80 lb bags of the 80 lb size. A deeper pour holds more too, and a bigger post leaves less around it. The waste allowance is added once, on the total, and the count is rounded up once, at the bag.
The maker's setting-posts sheet adds a gravel base to the hole depth; it is manufacturer guidance, quoted below, and it is not part of these counts.
Hole depth should be 1/3 the overall post length, plus 6" (150mm) for the gravel base.
Questions
How many bags of concrete for a 4x4 post?
The table gives the count for a 4x4 post in three hole widths and two depths of concrete, in three bag sizes. The fence post calculator counts your own sizes and the whole fence.
How many bags for a 2 ft deep hole?
The table's depth is the concrete only. For a deeper hole, enter its depth in the fence post calculator, which takes the gravel base off the hole depth.
Should I use 50 lb or 80 lb bags?
The table gives the count in each size so you can compare them. The larger bag makes more concrete per bag, so fewer are bought, and the count is rounded up once at the bag in either size.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Enter your hole and post in the fence post calculatorSources (1)
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QUIKRETE Setting Posts project sheet (opens in new tab), The Quikrete Companies, Undated project sheet.
Manufacturer data.
“Hole depth should be 1/3 the overall post length, plus 6" (150mm) for the gravel base.”
Per QUIKRETE's project sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.