Calculate concrete for footings whose dimensions have already been set. Choose a strip, isolated rectangular pad, or closed rectangular layout, then review each component and the combined order quantity without treating a material estimate as a footing design.
Select the footing geometry that matches your plan
A strip footing is a measured run with a width and thickness; an isolated footing is a rectangular pad with length, width, height, and a count. If the footing forms a closed rectangle, enter the outside dimensions and footing width so the inside opening can be subtracted. These options avoid forcing one repeated shape onto different foundation layouts. Dimensions should describe the concrete itself, not the excavation width or an assumed overdig.
For a strip footing, measure the net length of each run. At a corner, do not count the same intersection in both adjacent lengths. One approach is to use centerline lengths with a consistent junction rule; another is to divide the shape into non-overlapping rectangular pieces. Keep the plan geometry explicit, especially where cross-walls, steps, thickened sections, or attached pads meet. If heights or widths vary, calculate each zone separately and add the volumes.
Footing volume formulas
For a straight rectangular run, multiply length by width by thickness after converting all dimensions to feet. An isolated pad uses volume = length × width × height × quantity. For a closed rectangular strip footing with uniform width and depth, compute outer plan area minus inner plan area, then multiply by depth. The combined net volume is divided by 27 to express cubic yards. Each piece should be counted once, with no overlapping volume hidden in two line items.
The order quantity is calculated separately as net volume × (1 + allowance ÷ 100). The default concrete allowance is 10%, adjustable from the tool; it is neither a structural requirement nor a guarantee of sufficient material. If the footing is poured in multiple stages, you may choose a different allowance for planning, but the calculator must not quietly add it repeatedly to each piece and then to the total. The result should make clear whether it is net or includes allowance.
Worked example: a 40-foot strip footing
Suppose the measured net run is 40 ft, width is 24 in, and thickness is 12 in. Convert the width to 2 ft and thickness to 1 ft. The geometric volume is 40 × 2 × 1 = 80 ft³, equal to about 2.963 yd³. A 10% material allowance produces 88 ft³, or about 3.259 yd³ to plan for. The result is tied to the specified dimensions; it does not tell you whether they are appropriate for a building.
A closed rectangular example shows why corner treatment matters. For outside dimensions 20 ft by 10 ft, footing width 2 ft, and depth 1 ft, the interior dimensions are 16 ft by 6 ft. Outer area is 200 ft² and inner area is 96 ft², leaving 104 ft² of concrete plan area. At 1 ft deep, net volume is 104 ft³; with 10% allowance it is about 4.237 yd³. This subtracts the center opening and counts the four corners once.
Combine pads and runs without double counting
A foundation can include strip runs, isolated pads, and short connecting sections. Add each non-overlapping component to the total, or define how an intersection is allocated before entering the pieces. If a column or wall starts at the top of a footing, the above-footing height should begin at the footing top rather than overlapping the footing’s full depth. The same rule applies when transferring a footing quantity to a separate pier or wall material estimate.
The per-component breakdown is useful when ordering in stages or checking a drawing. It should show input dimensions, quantity, net volume, and how the allowance was applied. Do not round every small component to a whole cubic yard before adding; combine precise net volumes, apply allowance once, and then ask a supplier what increments it accepts. A bag count can be added using a named product yield, but the primary result remains the total volume relevant to a ready-mix order.
Estimate limits and structural decisions
A footing’s concrete quantity is not a bearing-capacity check. This page does not determine soil pressure, frost depth, reinforcement, building loads, settlement, footing width, wall support, or local code compliance. The user-provided dimensions should come from approved drawings or qualified local advice. A quantity tool should never convert an assumed house size or number of stories into a footing recommendation.
If you need a preliminary bearing-area calculation for a deck support, use the dedicated deck footing page and enter a known load together with a matching gross allowable soil pressure. That calculation returns an area equivalent only; it does not generate a construction-ready size. If you do not have the load or soil value, the right next step is to obtain those design inputs rather than guess. A correct cubic-yard result cannot compensate for missing design information.
Ordering and next steps
Before ordering, check the drawing revision, dimensions, concrete placement sequence, and any stepped elevations. Confirm whether the listed thickness is vertical depth and whether a footing tapers or includes a haunch that is not represented by a rectangle. Ask the supplier about minimum volume, partial loads, delivery access, and scheduling. This calculator supplies quantity only; a quoted ready-mix material price, delivery fee, and installation estimate are separate lines with different assumptions.
For a more complete foundation budget, use the foundation cost page’s project-type planning mode, or pass measured quantities to its detailed material path. Do not add a detailed footing-material estimate to a reference installed foundation budget that already includes concrete or related work. Keep the two results separate so the same footing material is not counted twice. For a slab above the footing, the slab calculator can estimate that distinct placement when its shape and dimensions are known.
Frequently asked questions
What dimensions do I need for a strip footing?
Enter the measured net length, width, and thickness. Use consistent units and avoid including the same corner intersection in two run lengths.
Can this calculate an isolated pad footing?
Yes. Enter its length, width, height, and quantity. Repeated pads are multiplied by the count, with the allowance applied to the combined net volume.
How does a closed rectangular footing avoid counting corners twice?
The method subtracts the interior plan area from the exterior plan area, then multiplies the remaining ring area by depth.
Does the calculator recommend footing dimensions?
No. It estimates volume for dimensions you provide. Loads, soil, frost depth, reinforcement, and local requirements need project-specific design input.
Is a footing quantity the same as a foundation estimate?
No. A measured footing volume is one material quantity. A foundation cost estimate may cover a broader system and may already include related work.
How much allowance should I use?
The page defaults to an adjustable 10% planning allowance. The appropriate amount depends on site and ordering conditions; it is not a mandated value.