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Construction

Concrete Spread Footing Calculator.

Estimates the volume of concrete needed for a spread footing and the required rebar length based on footing dimensions.

Results update live as you type.
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Your inputs

How it works

  1. 1

    Convert thickness from inches to feet by dividing by 12.

  2. 2

    Multiply length by width to get the footing area in square feet.

  3. 3

    Multiply the area by the thickness in feet to get the volume in cubic feet.

  4. 4

    Optionally, divide by 27 to get cubic yards for ordering concrete.

length * width * (thickness / 12)

Frequently asked questions

How do I convert cubic feet to cubic yards?

Divide the volume in cubic feet by 27, since there are 27 cubic feet in a cubic yard.

Should I add extra concrete for waste?

It's common to add 5-10% extra to account for spillage and uneven subgrade. Multiply your calculated volume by 1.05 to 1.10.

What is a spread footing used for?

A spread footing distributes the load of a column or wall over a larger area of soil to prevent settling.

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Results

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Concrete Volume

0cu ft

Concrete in Cubic Yards0cu yd
Rebar Length (perimeter)0ft
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Estimate for general guidance only — verify important decisions with an appropriate professional.

How it works

Estimates the volume of concrete needed for a spread footing and the required rebar length based on footing dimensions.

  1. Convert thickness from inches to feet by dividing by 12.
  2. Multiply length by width to get the footing area in square feet.
  3. Multiply the area by the thickness in feet to get the volume in cubic feet.
  4. Optionally, divide by 27 to get cubic yards for ordering concrete.

Formulas

The math behind this calculator, written out so you can verify the result.

Volume of Concrete

V = L × W × T

Multiply the length, width, and thickness (converted to feet) to get the volume in cubic feet.

Example:

Input: L = 8 ft, W = 6 ft, T = 12 in

Calculation: 8 × 6 × (12/12) = 48 cu ft

Result: 48 cubic feet

Rebar Perimeter

P = 2 × (L + W)

The perimeter of the footing gives the total length of rebar needed for edge reinforcement.

Example:

Input: L = 8 ft, W = 6 ft

Calculation: 2 × (8 + 6) = 28 ft

Result: 28 feet

Real-world use cases

Where this calculation shows up in everyday life.

Residential Foundation

Estimate concrete for a house foundation spread footings.

Example: A 30 ft by 40 ft house with footings around the perimeter.

Column Footings

Calculate concrete for individual column footings in a building.

Example: A 2 ft by 2 ft footing for a porch column.

Retaining Wall Base

Determine concrete volume for the base of a retaining wall.

Example: A 20 ft long wall with a 2 ft wide footing.

Tips and common mistakes

Tips

  • Always double-check your measurements before ordering concrete.
  • Consider adding 10% extra for waste and uneven ground.
  • Use the cubic yard result when ordering from a ready-mix supplier.
  • Rebar spacing and size should be determined by an engineer.

Common Mistakes to Avoid

  • Forgetting to convert thickness from inches to feet.
  • Using the wrong formula for volume (e.g., mixing units).
  • Not accounting for waste or over-excavation.

Assumptions and limitations

  • Use the stated inputs and units.
  • Results are estimates for planning and education.
  • Check measurements and source data before making an important decision.