Concrete Footing & Foundation Calculator: Yards & Bags
This concrete footing and foundation calculator sizes strip and wall footings by turning length, width and depth into cubic yards, bags and cost. Accurate footing volume matters because these pours carry the whole structure and can't be under-filled or interrupted.
Estimated concrete
Estimates only. Add ~5–10% for waste. Bag yields: 40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft. Concrete ≈ 150 lb per cu ft.
How the Concrete Footing & Foundation Calculator works
- 1
Enter your dimensions
Type the length, width and thickness of your slab, footing or pad and choose your units, feet, inches or meters.
- 2
Get instant volume
See the result in cubic yards, cubic feet and cubic meters, plus weight, the moment you type, no page reloads.
- 3
Buy the right amount
We convert volume into the exact number of 40, 60 and 80 lb bags, truck loads and cost so you order without waste or shortfalls.
The formula
Cubic yards = [Length_ft x (Width_in / 12) x (Depth_in / 12) x Count] / 27
- ·Length_ft = footing run length (feet)
- ·Width_in = footing width (inches)
- ·Depth_in = footing depth or thickness (inches)
- ·Count = number of identical footing runs
- ·27 = cubic feet per cubic yard
Width and depth are entered in inches and converted to feet by dividing by 12. Trenches are rarely dug perfectly, so adding 10% or more for over-dig is wise.
Worked examples
Example 1: 40 ft footing, 16 in wide, 8 in deep
- Width = 16 / 12 = 1.333 ft
- Depth = 8 / 12 = 0.667 ft
- Volume = 40 x 1.333 x 0.667 = 35.56 ft3
- Yards = 35.56 / 27 = 1.32 yd3
Result: About 1.32 cubic yards
Example 2: 60 ft footing, 12 in wide, 12 in deep
- Width = 12 / 12 = 1 ft
- Depth = 12 / 12 = 1 ft
- Volume = 60 x 1 x 1 = 60 ft3
- Yards = 60 / 27 = 2.22 yd3
Result: About 2.22 cubic yards
Concrete calculators by project type
Concrete bag yield & coverage
How much mixed concrete a standard bag yields, and how far a cubic yard goes at common slab depths.
| Bag size | Yield (cu ft) | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 | 90 |
| 60 lb | 0.45 | 60 |
| 80 lb | 0.60 | 45 |
- 40 lb
- 60 lb
- 80 lb
Related guides
Concrete footing & foundation calculator FAQs
How wide and deep should a concrete footing be?
A common residential footing is about twice the wall thickness wide and at least 8 inches deep, so a 16-inch-wide by 8-inch-deep strip is typical for an 8-inch wall. Always confirm size and frost depth with local code and your soil conditions.
How many yards of concrete for a 40-foot footing?
A 40 ft footing at 16 inches wide and 8 inches deep is 40 × 1.333 × 0.667 = 35.5 ft³, or about 1.3 cubic yards. Add 5–10% because footing trenches are rarely perfectly uniform.
What concrete mix ratio is best for footings?
Footings commonly use a 1:2:4 cement-sand-gravel mix, which balances strength and workability for below-grade structural pours. A stronger 1:2:3 mix is used where higher loads or engineered specs require it.
Should I order ready-mix or bag concrete for footings?
Because footings must be poured continuously to avoid cold joints, ready-mix is usually the safer choice for anything over a yard. Bagged concrete only makes sense for very short footings or small pier pads.
How much extra concrete should I add for uneven footing trenches?
Hand-dug or over-excavated trenches can hold noticeably more than the nominal size, so add about 10% to your calculated volume. If sidewalls are ragged or soft, budget even more to be safe.
How do I account for a footing and foundation wall together?
Calculate the footing and the wall as two separate rectangular volumes, then add them for a total order. This tool handles the footing; use the wall calculator for the stem wall and combine the yards.
How do I calculate concrete footing volume?
Multiply the run length in feet by the width and depth converted to feet (inches divided by 12). That gives cubic feet, and dividing by 27 gives cubic yards. A 50 ft footing 12 in wide and 10 in deep is 50 x 1 x 0.833 = 41.67 ft3, or 1.54 yd3.
How many 80 lb bags of concrete does a footing take?
Each 80 lb bag yields about 0.60 cubic feet, so divide the footing volume by 0.60 and round up. A small 10 ft footing 12 in wide and 8 in deep is 10 x 1 x 0.667 = 6.67 ft3, or about 12 bags. Beyond roughly one cubic yard, ready-mix is cheaper and faster.
Should the footing and slab be poured together?
A monolithic or thickened-edge pour combines the footing and slab in one placement, which saves labor and creates a continuous section. Separate footings are poured first and left to cure before walls go up. The calculator handles either as long as you enter each element's dimensions.
How much extra should I order for a rough footing trench?
Hand-dug or machine-dug trenches almost always end up wider and deeper than planned, so add at least 10% and up to 15% on soft or uneven ground. Over-dug soft spots can swallow a surprising amount of concrete. It is cheaper to have a little left over than to stop mid-pour.
How deep should a footing be below the frost line?
Footings should bear below the local frost line to prevent heaving, which ranges from a few inches in warm climates to 48 inches or more in cold regions. Check your local building code for the exact depth. Enter that total depth into the calculator to size the pour.
Can I use bagged concrete for footings?
Bagged concrete works fine for short footings or a few isolated pads, but the volume adds up quickly. A single cubic yard is about 45 of the 80 lb bags, which is a lot of mixing. For continuous footings over a yard, order ready-mix instead.
How wide should a footing be relative to the wall it supports?
A common rule is that the footing width is at least twice the wall thickness, so an 8-inch wall gets a 16-inch footing. Depth is usually equal to or greater than the wall thickness. Soil bearing capacity and load can require wider footings, so confirm with an engineer for heavy structures.