How do you calculate concrete for footings?
Footing volume = length × width × depth ÷ 27. A continuous footing 60 ft long, 16 inches wide, 8 inches deep: 60 × 1.333 × 0.667 ÷ 27 = 1.98 yards. For post footings, use the cylinder formula: π × r² × depth ÷ 27 — a 12-inch diameter, 36-inch deep pier takes 0.087 yards, about 4 bags of 80-lb mix.
Common footing sizes and volumes
| Footing | Dimensions | Concrete needed |
|---|---|---|
| Deck pier | 12 in dia × 36 in | 0.087 yd³ ≈ 4 bags (80 lb) |
| Fence post | 8 in dia × 24 in | 0.026 yd³ ≈ 2 bags (80 lb) |
| Continuous wall footing | 16 in wide × 8 in deep | 0.033 yd³ per linear foot |
| Garage frost footing | 24 in wide × 12 in deep | 0.074 yd³ per linear foot |
How to read this table
- Deck pier sits at the top of the table (12 in dia × 36 in) — 0.087 yd³ ≈ 4 bags (80 lb). If your situation looks like this row, plan against the upper half of the range rather than the midpoint.
- Fence post anchors the bottom (8 in dia × 24 in) — 0.026 yd³ ≈ 2 bags (80 lb). Treat this as the conservative case you should still be profitable at.
- The gap between the top and bottom row is roughly 4.5×. 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 "common footing sizes and volumes" table, the fastest way to use this page is to find the closest row, take its dimensions, then stress-test it ±30% before you build a plan on it.
Context
Footing dimensions aren't a guess: width and depth come from the load and your frost depth, which building codes set by county — 12 inches in the deep South, 48+ inches in Minnesota. Pouring above the frost line is the classic cause of heaved decks and cracked foundations. Call 811 before digging, and order footings and slab separately if the pour schedule differs — footings often need to cure before forming continues.
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
Rectangular volume for continuous footings; cylinder volume (πr²d) for piers. Frost-depth and sizing requirements reference the International Residential Code (IRC R403) as adopted with local amendments — verify with your building department.
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 do you calculate concrete for footings?
Footing volume = length × width × depth ÷ 27. A continuous footing 60 ft long, 16 inches wide, 8 inches deep: 60 × 1.333 × 0.667 ÷ 27 = 1.98 yards. For post footings, use the cylinder formula: π × r² × depth ÷ 27 — a 12-inch diameter, 36-inch deep pier takes 0.087 yards, about 4 bags of 80-lb mix.
Which option pays the most in the common footing sizes and volumes table?
Deck pier, at 12 in dia × 36 in (0.087 yd³ ≈ 4 bags (80 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?
Fence post at 8 in dia × 24 in (0.026 yd³ ≈ 2 bags (80 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 4.5×. 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?
Rectangular volume for continuous footings; cylinder volume (πr²d) for piers. Frost-depth and sizing requirements reference the International Residential Code (IRC R403) as adopted with local amendments — verify with your building department.
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.