Foundation Cost Calculator
A concrete slab is one of the first big costs in any building project, and ordering the right volume avoids both shortfalls and wasted loads. This calculator computes the slab volume from its length, width, and thickness, converts it to cubic yards (how ready-mix concrete is sold), adds a waste allowance you set, and multiplies by your local price per cubic yard. Because concrete prices and slab thickness depend on your region and design, both are editable inputs, so the estimate is the material cost for your specific slab.
Foundation cost formula
area = length * width (square feet)
volume = area * (thickness inches / 12) (cubic feet)
cubic yards = volume / 27
with waste = cubic yards * (1 + waste% / 100)
cost = cubic yards with waste * price per cubic yard
One cubic yard equals 27 cubic feet, and thickness is divided by 12 to convert inches to feet. The price per cubic yard is yours to set from a local quote.
Foundation facts
- Ready-mix concrete in the United States is ordered by the cubic yard (27 cubic feet).
- Residential slabs are commonly around 4 inches thick, subject to code and design.
- A waste allowance covers spillage, uneven subgrade, and rounding up to whole loads.
- This estimate is concrete material only; labour, rebar, forms, and base are separate.
- Always build to your structural engineer's specification and local building code.
Foundation cost: frequently asked questions
How do I estimate the cost of a concrete slab foundation?
Multiply the slab length by width to get area, multiply by thickness for volume, and convert to cubic yards (the unit concrete is sold in). Multiply the cubic yards, including a waste allowance, by your local price per cubic yard. Because concrete prices vary by region and supplier, the price is an input you provide.
How thick should a foundation slab be?
Slab thickness depends on the load and local building code. Residential slabs are often around 4 inches, while slabs carrying heavy loads are thicker. Always follow your engineer's specification and local code. This calculator takes thickness in inches as an input so you can match your design.
Why convert to cubic yards?
Ready-mix concrete in the United States is ordered and priced by the cubic yard. One cubic yard is 27 cubic feet. This calculator converts the slab volume from cubic feet to cubic yards by dividing by 27, then applies your price per cubic yard so the estimate matches how concrete is sold.
What does the waste allowance cover?
Some concrete is lost to spillage, over-excavation, uneven subgrade, and the practical reality that you must round up to whole or half loads. A waste allowance, often around 10 percent, ensures you order enough. You can set the percentage to match your site conditions and confidence.
Does this include labour, rebar, and forms?
No. This calculator estimates the concrete material cost only, based on volume and your price per cubic yard. Labour, reinforcing steel, formwork, excavation, gravel base, and finishing are separate line items. Add them to the concrete figure for a complete project budget.
Official sources
- National Institute of Standards and Technology (NIST): Volume unit conversion (cubic feet and yards).
- U.S. Department of Housing and Urban Development: Residential construction guidance.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.