Easy Masonry Calc

How much concrete for a metal fence post?

Short answer

A 1⅝ inch steel line post in an 8 inch hole 30 inches deep takes about 0.92 cubic feet of concrete with 10% extra: 3 bags of 50 lb fast-setting (2.5 bags exactly) or 2 of 80 lb.

How to work it out

  1. Hole 3.1416 × (8 in ÷ 2)² minus the post, × 30 in of concrete
  2. + 10% = 0.92 cu ft per post ÷ 0.375 cu ft per 50 lb bag = 2.5 bags per post
  3. One post: buy 3 bags

A steel post takes up almost none of the hole — about 2 square inches of an 8 in hole’s 50 — so nearly all of the hole is concrete. The bag count is set by the hole, not the post. Leave a slight dome on top of the concrete so water sheds away from the steel.

Adjust for your project

in
Quikrete’s rule of thumb: about 3 times the post width (10½ in for a 4×4, so a 10 or 12 in auger)
in
Quikrete: about ⅓ of the post’s total length. Local frost depth and fence rules come first
50 lb fast-setting ≈ 0.375 cu ft · 80 lb standard ≈ 0.60 cu ft
More options: Gravel · Top · Extra …
in
Many builders use 4–6 in of gravel for drainage; Quikrete’s own method uses none. 0 if none
in
Quikrete’s fast-setting method stops 3–4 in below the surface and finishes with soil or sod
%
Hand-dug holes are rarely neat cylinders — 10–15%
ft
$
Optional — an example figure; use your store’s price
Bags to buy3 bags50 lb bag
Bags per post
2.5 bags
If you share batches between holes
3 bags · 50 lb bag
Concrete for all posts
0.92 cu ft (0.0341 cu yd)
Quikrete’s rule of thumb for this post
Hole about 5 in wide and 28 in deep for a 7 ft post
  • Call 811 (in the US) or your local utility locate service a few days before you dig.
Check local rulesPost depth (often below the local frost line), fence height and setbacks are set by local rules — check with your building department or HOA before you dig.

For this job · affiliate link
Post levelA strap-on post level reads plumb on two faces at once, so you can set the post and walk away while fast-setting mix hardens.
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Line post in an 8 in hole, by depth

Line post in an 8 in hole, by depth
Hole depthBags per postConcrete for all posts
24 in2 bags0.74 cu ft
30 in2.5 bags0.92 cu ft
36 in2.9 bags1.1 cu ft
42 in3.4 bags1.29 cu ft

Line posts vs terminal posts

Chain-link fences use light line posts (often 1⅝ or 1⅞ in) along the run and heavier terminal posts (often 2⅜ in) at the ends, corners and gates, where the fabric is stretched. Terminal posts pull hard on their footings, so they normally get bigger, deeper holes; follow the fence maker’s instructions for each. A 2⅜ in post in a 10 in hole 36 in deep takes about 1.7 cu ft with the extra (variants below).

Fast-setting mix suits metal posts well: pour it dry around the braced post, soak it, and the post holds in under an hour. Leave a slight dome at the top so water sheds away from the steel.

A run of posts

For 100 ft of chain link with line posts about every 10 ft (check your kit), you need roughly 9 line posts and 2 terminals. At about 2.5 bags of 50 lb per line post and 5 per terminal, that is about 32 bags — more if you round up hole by hole. Wood posts follow the same math with a bigger post subtracted: how much concrete for a 4×4 post. For heavy gate posts, see how much concrete for a 6×6 post.

Different size? Use the full Fence Post Concrete Calculator.

What you’ll need

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Frequently asked questions

How much concrete for a 2⅜ inch chain-link terminal post?

About 1.7 cubic feet in a 10 inch hole 36 inches deep: 5 bags of 50 lb fast-setting.

How many bags of concrete for ten metal fence posts?

30 bags of 50 lb if each hole gets its own, or 25 bags sharing batches.

How much concrete for a 1⅞ inch line post?

About 0.91 cubic feet in an 8 inch hole 30 inches deep: 3 bags of 50 lb.

Other common sizes

Sources