How much concrete for a 12×12 footer?
A footer 12 inches wide and 12 inches deep holds 1 cubic foot of concrete per linear foot, so 27 feet of it is a cubic yard. Around a 12 × 12 ft building, 44 feet measured on the centre line, it takes 1.63 cubic yards, or 1.79 cubic yards with 10% extra (81 bags of 80 lb).
How to work it out
- 12 in × 12 in = 1 cu ft per foot × 44 ft = 1.63 cu yd
- + 10% = 1.79 cu yd (48.4 cu ft)
- ÷ 0.6 cu ft per 80 lb bag = 81 bags
“12×12 footer” gets searched two ways: a footing 12 inches by 12 inches in section, and the footing under a 12 by 12 foot shed, room or garage. The math below covers both, using a 12 × 12 in section around a 12 × 12 ft outline.
Adjust for your project
More options: Extra
- Or bags of mix (incl. extra)
- 81 bags · 80 lb bag
- Concrete before the extra
- 1.63 cu yd (44 cu ft)
- Concrete per linear foot
- 1 cu ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 6,380 lb (3 tons)
- Call 811 (in the US) or your local utility locate service a few days before you dig.
- Total to buy counts this as ready-mix. Switch “How will you buy it?” to bags if you are mixing it yourself.
- Over a yard: ready-mix is usually the practical choice. Have the trench inspected first if your permit requires it.
12 × 12 in footing at other lengths (10% extra)
| Total footing length | Concrete to order | Or bags of mix (incl. extra) |
|---|---|---|
| 20 ft | 0.81 cu yd | 37 bags |
| 36 ft | 1.47 cu yd | 66 bags |
| 44 ft | 1.79 cu yd | 81 bags |
| 60 ft | 2.44 cu yd | 110 bags |
| 92 ft | 3.75 cu yd | 169 bags |
| 100 ft | 4.07 cu yd | 184 bags |
Why 44 feet, not 48
The outside of a 12 × 12 ft building is 48 ft around, but a 12 in wide footing measured on its outside edge counts each corner square twice. Measuring along the centre of the footing — 11 ft per side — gives 44 ft, and that is the length that matches the concrete actually in the trench. The difference is 4 cu ft, about seven 80 lb bags.
At 1 cu ft per foot, 44 ft is 44 cu ft, or 1.63 yards. With 10% for a trench that is never perfectly square-sided, that is 1.79 yards: order 1.75 or 2 yards of ready-mix. In bags it is 81 of the 80 lb size, which is a lot for a trench you want poured in one go.
Is 12 × 12 the right size?
This page doesn’t answer that. Footing width and depth (and whether the bottom must be below the frost line) come from your plans and local code, and depend on the load and soil. A 12 × 12 in section is just a common example. If yours is different, change the width and depth above; a 16 in wide, 8 in deep footing over the same 44 ft takes about the same concrete, since 16 × 8 is close to 12 × 12 in area.
For the slab inside the footing, see how much concrete for a 12×12 slab, and for posts on round footings instead, how many bags of concrete for a 12 inch sonotube. A square pier of the same 12 × 12 in section holds the same 1 cu ft per foot of height — see how much concrete for a 12×12 column.
Different size? Use the full Concrete Footing Calculator.
What you’ll need
- Square-point shovelBudget price
Pushes and places concrete, and loads sand and gravel. The flat blade spreads a pour better than a round-point shovel.
See options on Amazon (opens in a new tab) - Portable electric concrete mixerPremium price
A small drum mixer turns a long day of hand-mixing into batches of two or three 80 lb bags. Check the drum size against the bag count you need.
See options on Amazon (opens in a new tab) - Rebar chairsBudget price
Hold rebar or mesh off the ground so it ends up inside the concrete, not under it. Match the chair height to where your plans place the steel.
See options on Amazon (opens in a new tab)
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Frequently asked questions
How much concrete for 100 feet of 12×12 footing?
3.7 cubic yards before extra and 4.07 cubic yards with 10%.
How much concrete for a 12×24 inch footing per 50 feet?
3.7 cubic yards, or 4.07 cubic yards with 10% extra.
How many 80 lb bags for a 12×12 footer 20 feet long?
37 bags with 10% extra (0.81 cubic yards).
Sources
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.
- NRMCA Concrete in Practice 31 — Ordering Ready Mixed Concrete (opens in a new tab) — Truck mixers carry 8 to 12 cubic yards (about 6 to 9 m³); order 4–10% more than the plan estimate; a loaded truck weighs about 80,000 lb; fresh concrete can cause severe chemical burns.
- NIST Handbook 44, Appendix C — General Tables of Units of Measurement (opens in a new tab) — 1 cubic yard = 27 cubic feet; 1 cubic foot = 1,728 cubic inches.
- 811 — Before You Dig (opens in a new tab) — The free national before-you-dig service; contact it a few business days before digging.