Footing Concrete Calculator
Enter the strip footing run and/or pad footings below.
Concrete
Concrete Footing Calculator
Quick answer: footing concrete (cubic yards) = length × width × depth in feet ÷ 27. A 100 ft strip footing 20 in wide and 10 in deep needs 5.14 yd³ — about 5.7 yd³ with 10% waste.
Estimate concrete for continuous (strip) footings under walls and square pad footings under posts and columns. Get cubic yards for a ready-mix order, bag counts for small pours, and an approximate material cost.
Footing cross-section
How to calculate concrete for footings
A footing is a rectangular block of concrete, so its volume is simply length × width × depth. The only traps are units (width and depth are usually measured in inches, length in feet) and waste (trenches are rarely dug to the exact design width).
L (ft) × W (ft) × D (ft) ÷ 27
= cubic yards of concrete (before waste)
- Measure the total run. For a perimeter footing, add all wall lengths measured along the centerline of the footing. Do not double-count corners.
- Convert width and depth to feet. Divide inches by 12 — 20 in = 1.667 ft, 10 in = 0.833 ft.
- Multiply length × width × depth for cubic feet.
- Add pad footings: count × side × side × depth (all in feet).
- Divide by 27 for cubic yards, then add 5–15% waste.
- Choose ready-mix or bags. Above roughly 1 yd³, a truck is usually cheaper and faster than mixing 45+ bags by hand.
Worked example
A 24 ft × 26 ft garage has a perimeter of 100 ft. The plan calls for a 20 in × 10 in footing plus four 24 in × 24 in × 12 in pads for interior posts.
- Strip footing: 100 × 1.667 × 0.833 = 138.9 ft³
- Pads: 4 × 2 × 2 × 1 = 16.0 ft³
- Total: 154.9 ft³ ÷ 27 = 5.74 yd³; with 10% waste = 6.3 yd³ → order 6.5 yd³.
Concrete per 10 feet of footing
Net volume before waste. Use it to sanity-check a quote or a takeoff.
| Footing size (W × D) | ft³ per 10 ft | yd³ per 10 ft | 80 lb bags per 10 ft |
|---|---|---|---|
| 12 in × 6 in (IRC minimum) | 5.0 | 0.19 | 9 |
| 16 in × 8 in | 8.9 | 0.33 | 15 |
| 20 in × 10 in | 13.9 | 0.51 | 24 |
| 24 in × 12 in | 20.0 | 0.74 | 34 |
| 30 in × 12 in | 25.0 | 0.93 | 42 |
Footing sizing and ordering tips
- Size comes from the code and the soil, not the calculator. The International Residential Code (IRC R403.1) sets a 12 in minimum width and 6 in minimum thickness, with wider footings for heavier loads or weak soils. Check your local building department.
- Get below the frost line. Footing bottoms must sit below the local frost depth — from about 12 in in the South to 48 in or more in northern states. Deeper trenches do not change footing volume, but they change stem-wall or pier height.
- Earth-formed trenches run wide. A backhoe bucket is often wider than the design. Measure the actual trench and use the real width, or raise waste to 15%.
- Watch short-load fees. Many ready-mix plants charge extra under 3–4 yd³. Combining footings with a slab or pier pour can avoid it.
- Rebar does not reduce volume. Steel displaces less than 1% of the concrete — ignore it in the volume calculation.
Footing concrete FAQ
How do you calculate concrete for a footing?
Multiply footing length × width × depth in feet to get cubic feet, then divide by 27 for cubic yards. For a 100 ft perimeter footing 20 in wide and 10 in deep: 100 × 1.667 × 0.833 = 138.9 cu ft ÷ 27 = 5.14 cubic yards, or about 5.7 yards with 10% waste.
How many bags of concrete do I need for a footing?
Divide the footing volume in cubic feet by the bag yield: about 0.60 cu ft per 80 lb bag, 0.45 cu ft per 60 lb bag, and 0.30 cu ft per 40 lb bag. A 2 ft × 2 ft × 1 ft pad (4 cu ft) needs about 7 bags of 80 lb mix.
How wide and deep should a footing be?
Under the International Residential Code, footings must be at least 12 inches wide and 6 inches thick, and the bottom must sit below the local frost line. Common residential footings are 16 to 24 inches wide and 8 to 12 inches thick, sized by soil bearing capacity and the number of stories.
How much extra concrete should I order for footings?
Add 5 to 10 percent for trenched footings with straight forms. Earth-formed trenches with uneven sides often need 10 to 15 percent because the trench is usually dug wider than the design width.
How we built this calculator: results use the standard volume, area, and coverage formulas shown on this page, with typical U.S. material densities, bag yields, and waste factors that you can override. Written and checked by the YardsCalculator editorial team. Last reviewed: October 2026.