Construction & Home

Foundation Calculator

Calculates the concrete volume for a rectangular foundation slab from its length and width in feet and its thickness in inches, giving the result in both cubic feet and cubic yards.

What this calculator does

The Foundation Calculator estimates your result instantly from the values you enter, using standard construction & home formulas. Calculates the concrete volume for a rectangular foundation slab from its length and width in feet and its thickness in inches, giving the result in both cubic feet and cubic yards. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.

Foundation Calculator

Result

—
Concrete (yd³)
—
Cubic Feet

About Foundation Calculator

This foundation calculator estimates how much concrete a rectangular slab needs. It multiplies length by width by thickness — converting the thickness from inches to feet — to get the volume in cubic feet, then divides by 27 to convert to cubic yards, the unit concrete is usually ordered in.

Formula & Mathematical Calculation

Concrete (yd³) = f(Length (ft), Width (ft), Thickness (in))

Calculated according to standard construction formulas implemented in the calculator core.

Calculation Example

For a slab 40 ft long, 30 ft wide, and 8 in thick:

  • Cubic feet = 40 × 30 × (8 ÷ 12) = 800 ft³
  • Cubic yards = 800 ÷ 27 = 29.63 yd³

Key Benefits

  • Reports concrete volume in both cubic feet and cubic yards for easy ordering
  • Handles thickness in inches and converts it to feet for you
  • Gives a quick material estimate before you price a concrete pour
  • Uses a plain rectangular slab formula so the math is easy to check

How to Use this Calculator

  1. Enter the length
    Type the slab length in feet into the Length (ft) field, for example 40.
  2. Enter the width
    Type the slab width in feet into the Width (ft) field, for example 30.
  3. Enter the thickness
    Type the slab thickness in inches into the Thickness (in) field, for example 8.
  4. Calculate
    Press Calculate to see the concrete volume in cubic yards and cubic feet.

Assumptions & Limitations

What the calculation assumes

  • Every value you enter is treated as an exact, known amount.
  • Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
  • Results use standard published formulas and account only for the values entered above.
  • Rounding is applied for display; the underlying calculation uses your full precision.
  • Results are returned in the same units you enter, unless the tool states the output unit.

What it does not cover

  • Foundation Calculator produces a calculated result for reference and learning, not a certified or official measurement.
  • Real-world outcomes differ when tolerances, rounding rules or local standards apply.
  • Definitions and standards vary by region and change over time; verify the convention that applies to your case.
  • Figures are only as accurate as the inputs you supply — check them before acting on the result.
  • For work where the result carries real consequences, confirm it against an authoritative source.

Frequently Asked Questions

Slabs are usually a few inches thick, so inches are easier to enter. The calculator divides the thickness by 12 to convert it to feet before finding the volume.

There are 27 cubic feet in a cubic yard, so the calculator divides the cubic-foot volume by 27. In the example, 800 cubic feet becomes about 29.63 cubic yards.

No. The figure is the exact geometric volume of the slab. Order a little extra to cover spillage, uneven subgrade, and over-excavation.

Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.