Concrete footing calculator (volume only)
Enter the footing size from your plans to see how many cubic yards or bags of concrete it takes. The calculator counts concrete; it does not size footings.
Enter your measurements
More options: Extra
- Or bags of mix (incl. extra)
- 88 bags · 80 lb bag
- Concrete before the extra
- 1.78 cu yd (48 cu ft)
- Concrete per linear foot
- 1 cu ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 6,960 lb (3 tons)
12 in × 12 in = 1 cu ft per foot × 48 ft = 1.78 cu yd
+ 10% = 1.96 cu yd (52.8 cu ft)
÷ 0.6 cu ft per 80 lb bag = 88 bags
- 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.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much concrete for a 12×12 footer | 1 cu ft per linear foot; 1.79 cu yd with 10% extra for 44 ft |
Your footing at other lengths
| Total footing length | Concrete to order | Or bags of mix (incl. extra) | Weight of the concrete (≈ 145 lb/cu ft) |
|---|---|---|---|
| 20 ft | 0.81 cu yd | 37 bags | 2,900 lb |
| 40 ft | 1.63 cu yd | 74 bags | 5,800 lb |
| 48 ft | 1.96 cu yd | 88 bags | 6,960 lb |
| 80 ft | 3.26 cu yd | 147 bags | 11,600 lb |
| 100 ft | 4.07 cu yd | 184 bags | 14,500 lb |
| 160 ft | 6.52 cu yd | 294 bags | 23,200 lb |
A footing (or footer) spreads the weight of a wall, post or slab edge over the soil. Its width, depth below grade and reinforcement are set by your plans and local building code — they depend on the load, the soil and how deep the ground freezes where you live. Once you have those dimensions, the concrete is simple arithmetic.
How to calculate concrete for a footing
continuous footing (cu ft) = length (ft) × width (in) × depth (in) ÷ 144 pad footing (cu ft) = length (in) × width (in) × thickness (in) ÷ 1,728 × number of pads cubic yards = cubic feet ÷ 27
For a continuous footing around a rectangle, measure along the centre line of the footing so the corners aren’t counted twice: 2 × (outside length + outside width) − 4 × footing width. For a 24 × 24 ft building with a 12 in footing that is 96 − 4 = 92 ft.
| Footing section | Cu ft per linear ft | Linear ft per cubic yard |
|---|---|---|
| 8 × 16 in | 0.89 | 30.4 |
| 10 × 20 in | 1.39 | 19.4 |
| 12 × 12 in | 1.0 | 27 |
| 12 × 24 in | 2.0 | 13.5 |
| 16 × 8 in | 0.89 | 30.4 |
Worked example
How much concrete for a 12×12 footer covers both readings of that search: a footing 12 in wide and 12 in deep, and the footing around a 12 × 12 ft shed or room.
Thickened slab edges
Many slabs on grade are poured with a turned-down, thickened edge instead of a separate footing. To count the extra concrete, enter the perimeter as the length, the thickened width as the width and only the depth below the slab bottom as the depth, then add the slab from the concrete calculator. The 24×24 garage slab works through this.
Round footings and piers
Deck and porch piers are usually round, formed with a fiber tube or poured into an augered hole. Use the Sonotube calculator for those; for a tube on top of a wider spread footing, add the pad here.
Tips
- Trenches cut by a backhoe bucket are usually wider than the footing on paper. Measure the actual trench, or add 15% or more.
- Pour on undisturbed or properly compacted soil, never on loose fill or frozen ground.
- Have the trench and any steel inspected before the pour if your permit calls for it — once concrete is in, it is too late.
- Footings are often poured with ready-mix. NRMCA suggests ordering 4–10% over the calculated volume.
What you’ll need
- 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) - Rebar tie wire and twisterBudget price
Ties bars together where they cross so the grid stays put while you pour.
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) - 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)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How deep and wide should a footing be?
That comes from your local building code and plans, not a calculator. Depth usually has to reach below the local frost line, and width depends on the load and soil. Ask your building department; this calculator only counts the concrete for the size they give you.
How much concrete per linear foot of footing?
Width (in) × depth (in) ÷ 144 gives cubic feet per foot. A 12 × 12 in footing is 1 cu ft per foot, so 27 ft of it is a cubic yard.
How many bags of concrete for a footing?
Work out the cubic feet and divide by the bag yield: about 0.6 cu ft per 80 lb bag. A 12 × 12 in footing takes about 1.7 bags of 80 lb per foot before waste — which is why most footings are poured with ready-mix.
Do I include the slab when the footing and slab are poured together?
Yes. Work out the slab with the concrete calculator, add only the extra depth below the slab here, and order the total.
Related guides
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.