Fence Ledger

Fence Ledger

How many bags of concrete for 30 fence posts?

Thirty posts is a large residential job — a long boundary or most of a small lot — and at this quantity concrete becomes a delivery question rather than a shopping trip.

Concrete needed
50 bags

80 lb bags, for 30 posts in 10 in holes 30 in deep on a 4 in gravel base. Change any of those and the count changes.

What the usual answer misses

At thirty posts the arithmetic stops being academic. The gap between the two-bags-per-post rule and a computed figure is large enough to change how you buy: enough bags to be worth a pallet delivery rather than a car boot, and enough weight that a wrong number means either paying for a second delivery or storing what you did not need through a wet season.

Work out your own

Every assumption above is editable. Change the length, the spacing, the hole size — the numbers and the working update as you go.

Units
Shape
Advanced options

These are typical values, not requirements. Post depth in particular is governed by your local frost line and building code — check before you dig.

Posts
31
Sections
29
Pickets
524
Concrete
52 bags

Estimated cost

Materials only (DIY)
$2,056 – $5,240
Professionally installed
$6,000 – $13,360

National planning ranges compiled from published US construction cost guides, last checked September 2026 (confidence: medium-low). Prices vary sharply by region, season and contractor. These are estimates for planning, not quotes.

Sources: homeguide.com, calcsummit.com, angi.com, ergeon.com, homewyse.com

Shopping list

Bill of materials for this fence
MaterialSizeQuantity
Posts4x431
Rails incl. waste2x496
Pickets incl. waste1x6524
Concrete mix52bags
Gravel12bags
Exterior screws≈3,400
Walk gate kit1

Why these numbers

How we got the section count
  1. Run 1: 228 ft ÷ 8 ft = 28.5, rounded up to 29 sections
How we got the post count
  1. 3 posts are fixed by the shape itself
  2. 2 at the open ends
  3. 1 carrying a gate
  4. 28 line posts spaced between them
  5. 31 posts in total
How we got the picket count
  1. Each picket covers 5.5 in plus a 0.25 in gap, so they repeat every 5.75 in
  2. 228 ft of fence needs 476 pickets
  3. Plus 10% for offcuts, rounded up to 524
How we got the concrete
  1. Each 10 in hole is 30 in deep, less 4 in of gravel base, leaving 26 in of concrete
  2. The 4x4 post itself takes up part of that, so each hole needs the remainder
  3. Across 31 posts
  4. Divided by the 0.6 cu ft a bag yields: 51.53, so buy 52 bags

Common questions

Is ready-mix worth it at this scale?
It starts to be worth pricing. Ready-mix removes the mixing entirely but arrives on its own schedule and has to be placed quickly, which suits a job where every hole is already dug and ready. Bags suit a job done over several weekends.
How should bags be stored between weekends?
Dry, off the ground and covered. Bagged cement absorbs moisture from the air and from a damp slab, and a bag that has gone hard in storage is waste rather than an inconvenience.
Does the mix strength matter for fence posts?
A standard general purpose mix is what most fence work uses. Higher strength mixes cost more and buy little here, because a fence post footing fails by the soil moving or the timber rotting long before the concrete is the limiting factor.