Concrete Calculator
Calculate concrete volume in cubic yards for slabs, footings, and pads.
What this tool does
Estimate concrete volume for rectangular pours such as slabs, pads, and footings. Output is shown in cubic yards for ready-mix ordering.
How to use
- Enter pour length and width in feet and depth in inches.
- Review the cubic yard estimate.
- Use the cement calculator to convert yards into bag counts if needed.
Formula
Cubic yards = (length ft × width ft × depth in ÷ 12) ÷ 27
Examples
10x20 slab at 4 inches
Input: Length: 20 ft, Width: 10 ft, Depth: 4 in
Output: Concrete needed: 2.47 cubic yards
Volume = 20 × 10 × (4/12) ft = 66.67 cu ft ÷ 27 = 2.47 cu yd.
Learn more
Slab volume formula
Rectangular pours: length × width × depth (feet) ÷ 27 = cubic yards. Depth is entered in inches and converted to feet.
Order 5–10% extra concrete for waste, uneven subgrade, and pump line loss.
Next steps in your pour plan
Convert cubic yards to bag counts with the cement calculator, or estimate gravel and mulch for adjacent site work.
Assumptions
- Pour shape is a rectangular prism.
- Depth is entered in inches and converted to feet before volume calculation.
- 1 cubic yard = 27 cubic feet.
Common use cases
- Estimate ready-mix orders for patios and sidewalks
- Plan footing volumes for small structures
- Compare slab thickness options before pouring
FAQ
Should I add extra concrete?
Yes. Order 5–10% more to account for spillage, uneven subgrade, and pump line waste.
Does this work for irregular shapes?
This version supports rectangular pours. Break irregular areas into rectangles.
What depth should I use for a patio?
Many residential patios use 4 inches; driveways often need 4–6 inches depending on load.
Source notes
- Standard ready-mix ordering unit in the US is cubic yards.
- Add 5–10% waste when placing your order.
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Last reviewed: 2026-06-02