Concrete Footing Calculator
Enter the footing length, width and thickness from your approved plan and get the concrete to order in cubic yards, the equivalent bag count, the weight of the pour and an optional cost. The waste allowance is added on top, the way ready-mix is actually ordered. This tool does not size the footing.
Concrete to order
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Results are estimates for planning purposes. Verify with your supplier, engineer, or a qualified professional before ordering material or performing work.
Concrete per linear foot of strip footing
| Footing | ft³ per linear foot | Linear feet per yd³ | 80 lb bags per foot | Weight per foot |
|---|---|---|---|---|
| 12 in × 6 in | 0.50 | 54.0 | 0.83 | 72 lb |
| 16 in × 8 in | 0.89 | 30.4 | 1.48 | 129 lb |
| 16 in × 10 in | 1.11 | 24.3 | 1.85 | 161 lb |
| 20 in × 8 in | 1.11 | 24.3 | 1.85 | 161 lb |
| 24 in × 8 in | 1.33 | 20.3 | 2.22 | 193 lb |
| 24 in × 12 in | 2.00 | 13.5 | 3.33 | 290 lb |
| 36 in × 12 in | 3.00 | 9.0 | 5.00 | 435 lb |
Arithmetic from the dimensions, before any waste allowance. Bag counts use the 0.60 ft³ yield of an 80 lb bag of QUIKRETE Concrete Mix; weight uses 145 lb/ft³. These are common footing sizes, not recommendations — the size for your building comes off the plan.
Before you order
- This tool does not size footings. Width, thickness, depth below grade and reinforcement follow from the load, the bearing capacity of the soil, the frost depth and the code your jurisdiction has adopted. Get them from a stamped plan or your building department, then come back here for the volume.
- Over-dig is the big one. A trench cut with a bucket is wider than the line on the plan, and every extra inch of width is concrete you pay for. NRMCA TIP 8, quoting ASTM C94, lists over-excavation of the subgrade alongside waste, spillage, air loss, settlement and form deflection as the reasons the truck comes up short. Formed footings can run a 5% allowance; trenched footings in soft ground often need 10% or more.
- Measure the concrete, not the trench. The thickness field is the depth of concrete. If the trench is 24 in deep and the footing is 8 in thick with backfill above it, enter 8.
- The stem wall is a separate pour. So is a thickened slab edge. Run each shape on its own and add the results.
- The trench itself is regulated. A footing excavation 5 ft deep or more needs a protective system under 29 CFR 1926.652(a)(1) unless it is cut entirely in stable rock, and a competent person has to inspect it before each shift.
How it's calculated
- Volume of one footing
V (ft³) = length (ft) × width (in) / 12 × thickness (in) / 12- Total volume
V total = V × number of footings → yd³ = ft³ / 27- Volume to order
V order = V total × (1 + waste % / 100)ASTM C94, quoted in NRMCA TIP 8, lists why the truck comes up short against a paper calculation: waste, spillage, loss of air content, settlement, form deflection and over-excavation of the subgrade. On a footing dug with a bucket, over-excavation is usually the biggest of the six.- Weight
weight (lb) = V total (ft³) × 145 lb/ft³Normalweight concrete runs 140 to 150 lb/ft³ (2,240 to 2,400 kg/m³); 145 is the midpoint used here.- Bags
bags = ceiling(V order (ft³) / yield per bag), yield = 0.30 ft³ (40 lb), 0.45 ft³ (60 lb), 0.60 ft³ (80 lb)Published yields for QUIKRETE Concrete Mix No. 1101. Yield varies by product — check the bag you buy.
Frequently asked questions
35.6 cubic feet, or 1.32 cubic yards of net volume. With a 10% waste allowance you would order about 1.45 cubic yards. In bags that is 66 of the 80 lb size.
4 cubic feet each, or 0.15 cubic yards. Twelve of them come to 48 cubic feet, 1.78 cubic yards net and about 1.96 cubic yards with a 10% allowance.
No, and no free calculator should. Footing width, thickness, depth below grade and reinforcement depend on the load, the soil bearing capacity, the frost depth and the building code your jurisdiction has adopted. Those numbers come off a stamped plan or from your building department. This tool converts the dimensions you were given into a concrete order.
A strip or continuous footing is a long, narrow ribbon of concrete under a wall, sized by the load per linear foot. A spread footing, also called a pad or isolated footing, is a square or rectangular block under a single column or post. Same arithmetic, different shape: one long run versus a number of identical pads.
Yes. A footing trench cut with an excavator bucket is almost never the exact width on the plan, and every inch of over-dig is concrete you pay for. That is one of the six reasons NRMCA TIP 8 gives, from ASTM C94, for the placed volume exceeding the calculated volume. If you formed the footing with lumber instead of digging to neat lines, a 5% allowance is usually enough; on a trench cut in soft ground, 10% or more is realistic.
No. Rebar displaces so little concrete that it is normally ignored. A stem wall or a foundation wall on top of the footing is a separate pour with its own dimensions — run the calculator again for it, or use the slab calculator. A keyway cut into the top of the footing slightly reduces the volume and is also normally ignored.
A cubic yard is 45 bags of 80 lb, about 3,600 lb to carry, open and mix. Most crews stop bagging somewhere around a cubic yard and price a short-load delivery instead, minimum load charge included. Bags still win for a handful of isolated pads on a site a truck cannot reach.
The footing is not, but the excavation it sits in is. Any trench 5 ft deep or more needs a protective system under 29 CFR 1926.652(a)(1) unless it is cut entirely in stable rock, and a competent person has to inspect it. Deep footing trenches on hillside and basement work routinely cross that line.
Sources & references
- QUIKRETE Concrete Mix No. 1101 — product data sheet (yield per bag: 0.30 ft³ at 40 lb, 0.45 ft³ at 60 lb, 0.60 ft³ at 80 lb; 2 in minimum thickness)
- NRMCA CIP 36 — Structural Lightweight Concrete (normalweight density 140–150 lb/ft³)
- NRMCA TIP 8 — Concrete Yield: why the placed volume exceeds the calculated volume, per ASTM C94
- 29 CFR 1926.652 — Requirements for protective systems: the trench the footing sits in is regulated even though the footing is not
Content checked against these sources — last reviewed August 28, 2026.