Concrete calculator

Concrete patio

Patio slab volume, ready-mix order and bag-equivalent estimate with visible allowance.

Calculator result and formula

Ready-mix order: 3.25 yd³

Formula: L × W × D × quantity ÷ 27 × (1 + waste) → ready-mix order

Formula ID: CONC-PATIO-001 · Version 1.0.0 · Published · Last reviewed Aug 26, 2026.

Inputs

  • Patio length: Finished patio length Default: 20.
  • Patio width: Finished patio width Default: 12.
  • Concrete depth: Specified finished slab thickness Default: 4.
  • Waste factor: Allowance for placement, spill and field variation Default: 8.

How this calculator works

Use finished patio dimensions and thickness to calculate net volume, allowance and ready-mix purchase quantity transparently.

  1. Measure finished patio length and width.
  2. Enter the concrete thickness required by the final project design.
  3. Use the order quantity as a planning baseline before supplier and site review.

Worked example: Example: a 20 ft × 12 ft patio at 4 in depth contains 2.96 yd³ before allowance; with 8% waste it rounds to 3.25 yd³.

Assumptions and limitations

  • Ready-mix quantity is rounded up to the next 0.25 yd³.
  • 60 lb and 80 lb bag yields are planning assumptions of 0.45 ft³ and 0.60 ft³ respectively; confirm the selected product label.
  • Truck-load equivalent assumes a 10 yd³ planning load, not supplier delivery capacity.
  • Waste is applied to net volume before purchase rounding.

Common mistakes to avoid

  • Confirm the measurement basis and units before using the result.
  • Keep waste or allowance visible and adjust it for the actual job conditions.
  • Confirm supplier packaging, delivery increments, specifications, and final site requirements before ordering.

Calculator disclaimer

This planning calculator does not determine structural design, code compliance, installation requirements, or guaranteed pricing. Confirm final requirements with the appropriate responsible professional, authority, manufacturer, and supplier.

Formula review and sources

Internal QA complete · independent external review pending · 1 source reference.

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