Calculate how much concrete you need for footings in cubic yards, cubic feet, bags, weight, and cost for strip, pad, square, and round pier footings.
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Concrete Footing Formula
The amount of concrete for a footing starts with the volume of the footing. The volume formula depends on the footing shape.
For a strip, rectangular, or square footing the volume is the cross section multiplied by the length:
For a round pier or sonotube footing the volume uses the circle area times the depth:
Convert cubic feet to cubic yards by dividing by 27:
CY = V(ft3) / 27
Estimate the number of bags from the volume, a waste allowance, and the yield of each bag:
Estimate the weight of the concrete from the volume and the mix density:
- V = total net volume in cubic feet after multiplying identical footings; known-volume mode uses the entered volume directly
- L = footing length or total run
- W = footing width
- D = footing thickness or depth
- Dia = diameter of a round pier footing
- H = depth or height of a round footing
- CY = volume in cubic yards
- W% = waste or overage allowance as a decimal
- Yield = volume one bag of mix produces (cubic feet)
- Density = assumed poured-concrete unit weight; the editable default is 150 lb/ft³, not a universal product value
Select the footing shape or known-volume mode at the top. Identical quantities multiply the geometric volume. Extra allowance is optional and defaults to zero; it is not added again in known-volume mode. Bag yield, density, price basis, assumed full-truck capacity and volume precision are available in the settings disclosure; collapsing it does not deactivate entered values. Bag-price costs use whole bags. The 10 yd³ truck default gives full-load equivalents, not a delivery schedule. Enter actual package yield for 20 kg or custom bags.
Concrete Bag Yields and Footing Reference
Bagged concrete is sold by weight, but you order by volume, so the yield per bag matters. The table lists approximate mixed yields for QUIKRETE No.1101; use the actual product label, especially for metric or custom packages.
| Bag size | Yield (cubic feet) | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.60 | 45 |
| 60 lb | 0.45 | 60 |
| 50 lb | 0.375 | 72 |
| 40 lb | 0.30 | 90 |
Compare local product prices, delivery minimums, fees and practical mixing needs when choosing bags or ready-mix.
| Footing type | Illustrative size, not design | Common use |
|---|---|---|
| Strip / wall | 16 in to 24 in wide, 8 in to 12 in thick | Foundation and load bearing walls |
| Square pad | 24 in to 36 in side, 12 in thick | Posts and columns |
| Round pier | 8 in to 16 in diameter | Decks and sonotube piers |
This quantity tool does not size a footing or check soil bearing, loads, reinforcement or frost conditions. Obtain the actual design for the project; the table is illustrative only.
Example Problems
Example 1: Square pad footing. You pour one square pad footing that is 3 ft on each side and 12 in (1 ft) thick. The volume is 3 * 3 * 1 = 9 cubic feet. In cubic yards that is 9 / 27 = 0.33 cubic yards. Using 80 lb bags at 0.60 cubic feet each with no waste, you need 9 / 0.60 = 15 bags.
Example 2: Strip footing with allowance. For a 40 ft run, 20 in width and 10 in thickness, use the exact fractions: 40 × (20/12) × (10/12) = 55.5556 ft³ approximately. Multiply by 1.10 for a 10 percent allowance: 61.1111 ft³, or 2.2634 yd³ approximately (displayed as 2.26 at two decimal places). Supplier order increments are separate.
FAQ
How much extra concrete should I order for footings? Choose allowance with the contractor or supplier for actual trench variation, measurement uncertainty and placement losses. Blank means zero in this calculator; any selected allowance is a planning assumption, separate from supplier order increments.
Should I use bags or ready mix concrete? Compare package yield, total quantity, mixing needs and the supplier quote, including delivery fees and minimums. The calculator estimates material quantities and user-entered prices; it does not assume one supply method is cheaper at a universal threshold.
How much does concrete for a footing weigh? At the illustrative density of 150 lb/ft³, one cubic yard weighs 4,050 lb. Actual mix density varies; replace the default when known. Multiply your footing volume in cubic feet by 150 to estimate the poured weight, which is useful for planning delivery and support.
