Construction

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Construction

Concrete Porch Calculator.

Estimates the volume of concrete needed for a rectangular porch slab in cubic yards.

Results update live as you type.
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Your inputs

How it works

  1. 1

    Measure the length and width of the porch in feet.

  2. 2

    Measure the thickness in inches.

  3. 3

    Multiply length by width by thickness (converted to feet).

  4. 4

    Divide by 27 to get cubic yards.

round((length * width * (thickness / 12)) / 27 * 100) / 100

Frequently asked questions

How do I convert inches to feet?

Divide the thickness in inches by 12 to get feet.

Why divide by 27?

There are 27 cubic feet in one cubic yard.

Should I order extra concrete?

It's common to order 10% extra to account for spillage and uneven subgrade.

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Results

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Concrete Volume

0cu yd

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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 rectangular porch slab in cubic yards.

  1. Measure the length and width of the porch in feet.
  2. Measure the thickness in inches.
  3. Multiply length by width by thickness (converted to feet).
  4. Divide by 27 to get cubic yards.

Formulas

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

Volume in cubic yards

V = (L × W × T) / 324

L and W are in feet, T is in inches. Dividing by 324 converts cubic inches to cubic yards.

Example:

Input: L=10 ft, W=8 ft, T=4 in

Calculation: (10 × 8 × 4) / 324 = 320 / 324

Result: ≈ 0.99 cu yd

Real-world use cases

Where this calculation shows up in everyday life.

Planning a new porch

Estimate concrete needed before ordering from a ready-mix supplier.

Example: A 10x8 ft porch with 4-inch slab.

Budgeting materials

Calculate cost by multiplying volume by local concrete price per cubic yard.

Example: 0.99 cu yd × $150/cu yd ≈ $148.50

Comparing slab thickness

See how changing thickness affects concrete volume and cost.

Example: Increasing from 4 to 6 inches adds about 0.5 cu yd for a 10x8 slab.

Tips and common mistakes

Tips

  • Measure to the nearest 0.1 foot for accuracy.
  • Add 10% extra for waste and uneven ground.
  • Check local building codes for minimum thickness.
  • Use a concrete calculator for irregular shapes separately.

Common Mistakes to Avoid

  • Forgetting to convert thickness from inches to feet.
  • Using square feet instead of cubic feet.
  • 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.