Concrete Footing Calculator
To pour a 10 ft long × 1 ft wide footing at 8 in deep (the default footing depth) you need about 0.25 cu yd of concrete plus 10% waste — roughly 13 bags of 80 lb concrete mix.
Reviewed by The ponderloop teamUpdated 2026-07-11How we calculate
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0 cu yd + 0% waste = 0 cu yd
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How this number is calculated
0 cu yd (no waste added) ÷ 0.0222 cu yd per bag = 0 bags
Shopping list
- 80 lb concrete mix bag
- Mixing tub
- Finishing trowel
- Rebar (1/2 inch)
- Post level
- Concrete tube form (Sonotube)
0.0 cu yd — ~0% of a standard truck load
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Methodology & assumptions
Volume is calculated as footing length × width × (depth in inches ÷ 12), then divided by 27 to convert cubic feet to cubic yards. A waste percentage is added for spillage and over-digging, and the result is divided by the coverage per bag (about 0.0222 cu yd for an 80 lb bag) and rounded up to the next whole bag. For long footing runs that push the total past roughly 1 cubic yard, ready-mix delivery is usually more economical than bags.
- ACI 318 concrete practice (waste allowance)
- Manufacturer bag-yield specs (80 lb ≈ 0.60 cu ft)
- Typical US ready-mix and bag price ranges, 2026
Worked examples
| Room | Result |
|---|---|
| 10 × 1 ft footing, 8 in deep, standard waste | 0.25 cu yd + 10% waste ≈ 0.27 cu yd → 13 bags |
| 20 × 1.5 ft perimeter footing, 8 in deep, standard waste | 0.74 cu yd + 10% waste ≈ 0.81 cu yd → 37 bags |
| 6 × 2 ft pier footing, 12 in deep, minimal waste | 0.44 cu yd + 5% waste ≈ 0.47 cu yd → 22 bags |
Frequently asked questions
- How many bags of concrete do I need for a footing?
- Multiply the footing length by its width in feet, multiply by the footing depth (converted from inches to feet), and divide by 27 to get cubic yards. Add 10% for waste, then divide by the coverage per bag (about 0.0222 cu yd for an 80 lb bag) and round up.
- How deep should a footing be?
- It depends on your local frost line and code requirements — deck and fence post footings are commonly poured 8-12 in deep (sometimes deeper below the frost line), while a foundation wall footing is often deeper still. Check your local building code before pouring; this calculator defaults to 8 in as a common starting point, not a code recommendation.
- Does bag size (40 lb, 60 lb, or 80 lb) change how many bags I need?
- Yes. A 40 lb bag yields about 0.011 cu yd, a 60 lb bag about 0.0167 cu yd, and an 80 lb bag about 0.0222 cu yd. This calculator assumes 80 lb bags; if you are buying 40 lb or 60 lb bags, divide the cubic yardage by that bag’s yield instead to get an accurate bag count.
- Should I use ready-mix instead of bags for a large footing?
- Once a pour needs more than about 1 cu yd of concrete, a ready-mix truck (or a local mini-mix delivery) is usually cheaper per yard and far less labor than mixing dozens of bags by hand. Long runs of continuous footing (like a full foundation perimeter) are good candidates for ready-mix even if a single post footing is not.
- Do I need rebar in a footing?
- Most footings that carry structural load (deck posts, fence posts, foundation walls) benefit from at least one or two lengths of rebar run through the pour for tensile strength, and local code may require it. This calculator estimates concrete volume only — it does not size rebar for you.