Concrete Footing Calculator

A concrete footing calculator returns a strip footing as cubic yards, a ready-mix order rounded up to the nearest quarter yard, and a bag count for 40, 60 or 80 lb bags. It multiplies length, width and depth, then adds an 8% waste allowance by default. It does not size the footing.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Concrete Needed (with waste)

1.60 cu yd

Includes a 8% waste allowance.

Shopping list

Concrete mix72 80 lb bagsRounded up from 72.0 bagsOr 1.75 cu yd of ready-mix delivered.
Either

Bagged vs. Ready-Mix

Borderline range: bagged concrete works but means a lot of mixing for a continuous pour. A trench footing should generally be filled in one session to avoid cold joints, so call a local ready-mix plant for a short-load quote before committing to bags.

Breakdown
Concrete Needed (with waste)	1.60 cu yd
Total Volume (with waste)	43.2 cu ft
Bags Needed	72 bags (80 lb)
Ready-Mix Order Size	1.75 cu yd
Estimated Cost (Bags)
Estimated Cost (Ready-Mix)

How to Calculate Concrete Footing

A strip footing is a continuous trench of concrete, so its volume is just Length × Width × Depth. Width and depth are converted from inches to feet first, since they're usually specified that way on a plan. This calculator does not size the footing for you. Width and depth for a load-bearing footing come from your local building code or an engineer's design, based on soil type and the load above it, not from a generic formula. Once you have those dimensions, the same NRMCA ordering guidance used for a slab applies. Add 4-10% for spillage, an uneven trench bottom, and placement loss. This calculator defaults to 8% since a hand-dug trench is typically less uniform than a formed slab subgrade. The waste-adjusted volume is then expressed as cubic yards (÷27) for a ready-mix order, rounded up to the nearest quarter yard. It can also be expressed as a bag count using the same 40/60/80 lb yield figures as the Concrete Slab calculator.

Example: 40 linear feet of footing, 12 inches wide and 12 inches deep

40 linear feet of footing, 12 inches wide and 12 inches deep, at 8% waste, using 80 lb bags: 1. Width in feet: 12 ÷ 12 = 1.0 ft 2. Depth in feet: 12 ÷ 12 = 1.0 ft 3. Raw volume: 40 × 1.0 × 1.0 = 40.0 cubic feet 4. With 8% waste: 40.0 × 1.08 = 43.2 cubic feet 5. Cubic yards: 43.2 ÷ 27 = 1.60 cubic yards 6. Ready-mix order size, rounded up to the nearest ¼ yard: 1.75 cubic yards 7. Bags (80 lb, 0.60 cu ft each): 43.2 ÷ 0.60 = 72 bags At 1.6 cubic yards, this footing is in the calculator's "borderline" range. 72 bags is a lot of continuous hand-mixing for a trench pour, so a short-load ready-mix quote is worth getting before deciding.

Concrete Footing: Compare Scenarios

Scenario	Concrete Needed (with waste)	Total Volume (with waste)	Bags Needed	Ready-Mix Order Size
Small (20 ft shed footing)	0.80 cu yd	21.6 cu ft	36 bags (80 lb)	1.00 cu yd
Medium (40 ft foundation footing)	1.60 cu yd	43.2 cu ft	72 bags (80 lb)	1.75 cu yd
Large (150 ft foundation footing, 16 in. wide/deep)	10.67 cu yd	288.0 cu ft	480 bags (80 lb)	10.75 cu yd

What Is Concrete Footing?

A concrete footing calculator converts the dimensions of a strip (trench) footing into a purchasable quantity of concrete: cubic yards for a ready-mix order, or a bag count for hand-mixing. A footing is the buried, widened base a foundation wall sits on. It's distinct from a flat slab, since it's long and narrow rather than broad and thin. That's why it gets a length × width × depth calculation instead of the length × width × thickness used for a slab.

Concrete Footing: Pros and Cons

Pros

Applies a slightly higher default waste allowance (8%) than a flat slab, reflecting the less-uniform trench bottom typical of a footing dig
Shows both the bagged-mix and ready-mix path side by side so labor and delivery minimums can be weighed against cost
Rounds to what you can actually buy: whole bags, and the quarter-yard increments a ready-mix plant sells in

Cons

Does not determine footing width or depth. Those come from your local building code or a structural engineer based on the load and soil, and this calculator deliberately doesn't guess at them
Assumes a uniform cross-section along the full length. A stepped footing on sloped ground needs each section calculated and added separately
Does not size reinforcement (rebar). See the Rebar Material calculator once bar size and spacing are known

Concrete Footing: What a Pro Checks

Get your footing width and depth from your local building code or an engineer's design before running this calculator. It deliberately doesn't guess at those numbers, since they depend on the load above and your soil's bearing capacity.
Plan for one continuous pour if you can. A cold joint partway along a trench footing is a weak point in a way it usually isn't for a flat slab. That's why this calculator's default waste allowance (8%) runs higher than the Concrete Slab calculator's 5%.
Check whether your footing needs rebar before you order concrete. Most residential footings do, per local code, and the Rebar Material calculator can size that once you know bar size and spacing.

Frequently Asked Questions

How wide and deep should my footing be?

This calculator doesn't set that for you. Footing width and depth depend on the load above it, your soil bearing capacity, and your local frost depth and building code, and typically require a permit-reviewed plan or an engineer's design. Enter the dimensions from your approved plan and this calculator will tell you how much concrete that pour needs.

How much extra concrete should I order for a footing?

This calculator defaults to 8%, a bit above the NRMCA's general 4-10% guidance for ready-mix ordering, because a hand-dug trench bottom is typically less even than a formed slab subgrade. Use closer to 10% for a rough or unshored trench, or if the soil is loose enough that the sides may slough in before the pour.

Should I pour a footing with bagged concrete or order ready-mix?

Under about 1 cubic yard, bagged concrete is usually practical. Above about 3 cubic yards, ready-mix is almost always cheaper and less labor. A footing pour benefits more from a single continuous placement than a slab does, since a cold joint partway along a trench is a weak point. Factor that into the decision even in the borderline range.

Is a footing the same as a slab?

No. A slab is a broad, thin, flat pour (a patio, a garage floor). A footing is a narrow, deep, continuous trench that a foundation wall or column sits on. Use the Concrete Slab calculator for the flat portion of a project and this one for the footing underneath a wall, and add the two volumes together if your project needs both.

Does this include the foundation wall or stem wall above the footing?

No. This calculates only the footing itself. If your project also has a poured or block stem wall on top of the footing, calculate that volume separately. See the Concrete Slab calculator's approach for a poured wall, or the Concrete Block calculator for a block wall. Then add it to this result.

Do I need rebar in a footing?

Most residential footings are reinforced with continuous rebar per local code, but bar size, number of bars, and placement depend on your jurisdiction's requirements and the engineer's or plan's specification. This calculator only covers the concrete volume. Once you know the bar size and spacing, use the Rebar Material calculator to get a length and count.

Sources

Concrete & Masonry