Measure The Foundation Before You Pour
Use this Concrete Foundation Calculator to estimate concrete for slab foundations, strip footings, isolated footings, pads, and foundation wall systems. Calculate cubic feet, cubic yards, approximate bag quantities and optional ready-mix cost from your actual project dimensions.
Calculate slab foundations, strip footings, isolated footings or a combined foundation wall and footing. Results remain hidden until you press Calculate.
Estimate concrete for a rectangular slab foundation using finished length, width and slab thickness.
Material estimate only. Slab thickness, reinforcement, vapor barrier, base preparation, edge details and structural design must come from the applicable project requirements.
Estimate a continuous rectangular footing using total footing length, footing width and footing depth.
This calculator models the footing as a constant rectangular section. Stepped footings, keyways, grade beams and varying widths should be calculated separately.
Estimate several identical rectangular pad footings used below posts, columns or piers.
Use this option only for identical pad footings. Different footing sizes should be calculated in separate groups and added together.
Estimate a poured concrete foundation wall together with a continuous footing below it.
The wall is modeled as solid concrete with no door, window or utility openings deducted. Pilasters, steps, keyways and wall thickenings should be added separately when present.
Calculate rectangular foundation slabs from area and thickness.
Estimate continuous footing concrete from length, width and depth.
Calculate several identical column or pier foundations in one total.
Add a local ready-mix price for a basic concrete-material estimate.
A concrete foundation can contain several separate components, and each component should be measured using the geometry that actually applies to it. The Concrete Foundation Calculator provides four common options so you can estimate the major concrete sections independently rather than forcing the entire project into one simple shape.
Use Slab Foundation for a rectangular slab-on-grade or mat-like slab. Use Strip Footing for a continuous footing beneath walls. Use Isolated Footings for repeated pads beneath posts, columns or piers. Use Wall + Footing when the project contains a poured concrete wall supported by a continuous concrete footing.
Separate the slab, continuous footings, pads and walls shown on the project.
Use finished concrete length, width, height and depth rather than excavation size.
Select the calculator that matches each foundation component.
Apply a planning allowance for form variation, subgrade and placement loss.
Compare calculated volume with supplier minimums and project requirements.
Most foundation components can be estimated using rectangular-prism volume: length × width × depth. The main challenge is keeping units consistent because footing widths and depths are often shown in inches while plan dimensions are shown in feet.
Convert inches to feet by dividing by 12 before multiplying.
For repeated isolated footings, calculate one footing and multiply by the number of identical units. For a wall-and-footing system, calculate wall volume and footing volume separately, then add them.
A rectangular slab foundation is calculated from slab length × slab width × slab thickness. For example, a 30 ft × 20 ft slab has an area of 600 square feet. At 6 inches thick, the geometric concrete volume is 300 cubic feet, which equals approximately 11.11 cubic yards before any ordering allowance.
A slab foundation can include thickened edges, interior beams, grade beams, turndowns or column pads. Those deeper sections should be calculated separately instead of applying the deepest thickness to the entire slab.
For detailed slab-only comparison, use the Concrete Slab Thickness Calculator.
A strip footing is a continuous concrete element running below a wall or around a foundation perimeter. The volume formula is total footing length × footing width × footing depth.
Convert footing width and depth from inches to feet before calculating cubic feet.
If the footing steps down with grade, changes width, or includes thickened sections, divide the footing into segments and calculate each section independently.
Isolated footings are commonly used beneath posts, columns and piers. If all pads are identical, calculate one footing volume and multiply it by the number of footings. If the footing sizes differ, create separate groups based on size.
A 3 ft × 3 ft footing that is 12 inches deep contains 9 cubic feet of concrete. Eight identical footings contain 72 cubic feet, or approximately 2.67 cubic yards before allowance.
For cylindrical pier foundations instead of rectangular pads, use the Concrete Pier Calculator.
A poured foundation wall and its footing should be calculated separately because the wall is usually narrow and tall while the footing is wider and shallow. The calculator adds both components into one total.
Openings, pilasters and special wall sections are not automatically included.
Large openings can reduce concrete volume, while wall pilasters, steps and thickened corners can add volume. Use the project's actual geometry for a detailed estimate.
Foundation quantity is easiest to estimate by separating slab, wall and footing geometry into measurable concrete sections.
Foundation excavations and forms can vary slightly from the ideal dimensions. Soil can slough, trenches can be wider than expected, and placement can involve some loss. The calculator includes 0%, 5%, 10% and 15% ordering allowances so you can compare geometric volume with a practical order quantity.
The best allowance depends on the foundation type, form accuracy, excavation condition and supplier ordering increments. A formed wall may be more predictable than concrete placed directly into an irregular trench.
Each foundation calculator includes an optional price per cubic yard. Enter a local ready-mix rate and the calculator multiplies the adjusted concrete quantity by that rate.
This is a concrete-material estimate only. It does not automatically include excavation, stone base, reinforcement, forms, waterproofing, drainage, anchor bolts, insulation, pumping, delivery surcharges, labor, backfill or engineering.
Small isolated footings or repair pads can sometimes be placed with bagged concrete. The slab calculator includes approximate planning yields for common bag sizes. Large foundations, continuous strip footings and wall systems usually require enough concrete that ready-mix is the more practical quantity format.
Always verify bag yield on the actual product and check ready-mix supplier minimum-order and delivery requirements before scheduling a pour.
Excavation can include working room, gravel base or drainage layers. Calculate the actual concrete section.
Foundation wall concrete and footing concrete are separate volumes and both must be included.
Thickened slab zones should be added as extra volume rather than ignored.
Projects can contain several footing sizes. Group them by dimension for better accuracy.
A stepped footing on sloping ground can contain more concrete than one level rectangular strip.
The tool estimates material only and does not determine foundation bearing capacity or structural adequacy.
The calculator uses standard rectangular volume formulas. Its arithmetic is accurate for the dimensions entered, but actual foundation quantity can differ where excavations are irregular, walls contain openings, footings step, or structural sections vary.
For technical concrete information, visit the American Concrete Institute and the National Ready Mixed Concrete Association. For general concrete shapes beyond foundations, use the Concrete Calculator.
You can return to the Concrete Foundation Calculator above to compare slab, footing and wall dimensions before ordering concrete.
Common questions about slab foundations, strip footings, isolated footings, foundation walls, cubic yards and material cost.