How much concrete do you need per fence post?
A standard 4×4 post in an 8-inch diameter, 24-inch deep hole needs about 0.026 cubic yards — one to two 50-lb bags. The rule of thumb: hole diameter should be 3× the post width, and depth should be one-third of the post's above-ground height plus 6 inches of gravel.
Concrete per post by hole size
| Post / hole | Hole volume | Bags needed |
|---|---|---|
| 4×4 post, 8 in × 24 in | 0.70 ft³ | 2 × 50-lb or 1 × 80-lb + gravel |
| 6×6 gate post, 12 in × 36 in | 2.36 ft³ | 4 × 60-lb or 3 × 80-lb |
| Mailbox, 8 in × 18 in | 0.52 ft³ | 1 × 60-lb |
| Pergola post, 12 in × 48 in | 3.14 ft³ | 6 × 60-lb |
How to read this table
- Pergola post, 12 in × 48 in sits at the top of the table (3.14 ft³) — 6 × 60-lb. If your situation looks like this row, plan against the upper half of the range rather than the midpoint.
- Mailbox, 8 in × 18 in anchors the bottom (0.52 ft³) — 1 × 60-lb. Treat this as the conservative case you should still be profitable at.
- The gap between the top and bottom row is roughly 6.0×. That spread is why a single blended average is close to useless here — pick the row that matches your setup instead of averaging the column.
- With 4 reference points in the "concrete per post by hole size" table, the fastest way to use this page is to find the closest row, take its hole volume, then stress-test it ±30% before you build a plan on it.
Context
Deeper beats wider for stability: a 36-inch-deep post resists frost heave and wind load far better than a wide shallow one. Fast-setting mix is the right product here — it sets in 20–40 minutes without bracing. In frost zones, bell the bottom of the hole or use a formed pier so the freeze can't grab the smooth sides and jack the post upward; slope the top of the concrete away from the post so water doesn't pool against the wood.
What moves this number
Regional pricing
Ready-mix, bag, and labor prices vary 30–50% between US metros. Sun Belt markets with many plants run well below Northeast and remote-area pricing.
Waste and site conditions
Uneven subgrade, spillage, and form bowing consume 5–15% extra material. Orders placed at exact volume routinely come up short mid-pour.
Local code requirements
Frost depth, footing dimensions, and reinforcement rules are set by county. The same project can require twice the concrete in a northern climate versus a southern one.
Methodology
Cylinder volume πr²d minus post displacement, converted to bag counts at published yields (50-lb ≈ 0.375 ft³, 60-lb ≈ 0.45 ft³, 80-lb ≈ 0.60 ft³). Depth guidance follows the one-third rule and IRC frost-depth requirements.
Assumptions and caveats
- Volumes are theoretical; order quantities include a waste allowance but site conditions vary.
- Prices reflect 2026 US national ranges — get local quotes before budgeting a real pour.
- Structural dimensions and frost depths are governed by local building code; verify with your building department.
- This page was last reviewed on 2026-10-01. Ranges are updated as new data lands, so re-check before using them in a contract or a plan.
- Use these numbers as a starting range, not a guarantee — your own historical data always beats a benchmark.
Frequently asked questions
How much concrete do you need per fence post?
A standard 4×4 post in an 8-inch diameter, 24-inch deep hole needs about 0.026 cubic yards — one to two 50-lb bags. The rule of thumb: hole diameter should be 3× the post width, and depth should be one-third of the post's above-ground height plus 6 inches of gravel.
Which option pays the most in the concrete per post by hole size table?
Pergola post, 12 in × 48 in, at 3.14 ft³ (6 × 60-lb). That row represents the strongest case in this dataset, so use it as an upper bound rather than an expectation.
What is a realistic low-end figure?
Mailbox, 8 in × 18 in at 0.52 ft³ (1 × 60-lb). Plan your costs so the low end still works, then treat anything above it as upside.
Why do the numbers vary so much?
The spread between the highest and lowest row is about 6.0×. Regional pricing and waste and site conditions explain most of that gap — see the drivers section above for the full list.
Where do these numbers come from?
Cylinder volume πr²d minus post displacement, converted to bag counts at published yields (50-lb ≈ 0.375 ft³, 60-lb ≈ 0.45 ft³, 80-lb ≈ 0.60 ft³). Depth guidance follows the one-third rule and IRC frost-depth requirements.
How can I estimate my own number instead of using a benchmark?
Use the Concrete Cost Calculator on RevenueLab — it takes your own inputs and returns a figure specific to your setup, which is always more accurate than a published range.
Model your own numbers
Related reading
More answers in this category
- How do you calculate cubic yards of concrete?
- How many bags of concrete make a cubic yard?
- How do you calculate concrete for a slab?
- How do you calculate concrete for a driveway?
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Last updated 2026-10-01.