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.
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.
- Measure finished patio length and width.
- Enter the concrete thickness required by the final project design.
- 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 questions
- Does it determine reinforcement or joint spacing?
- No. This calculator only estimates volume; construction detailing needs independent review.
- Why use an allowance?
- Placement, spill and field variation can make a pure net-volume order too small.
Reference notes
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