Concrete Calculator
Pouring a slab, footing or pad? Enter the dimensions to get the concrete volume in cubic yards — how ready-mix is ordered — plus the number of 60 lb or 80 lb bags if you are mixing it yourself.
Your numbers
Result
- 60 lb bags
- 82
- Volumecubic feet
- 36.67
| Item | Amount |
|---|---|
| Volume | 1.36 cu yd (36.7 cu ft) |
| 80 lb bags | 62 |
| 60 lb bags | 82 |
How the volume is calculated
Volume is length × width × thickness, with the thickness converted from inches to feet. A 10 ft × 10 ft slab at 4 inches is 10 × 10 × (4 ÷ 12) = 33.3 cubic feet. Concrete is ordered by the cubic yard, and there are 27 cubic feet in a yard, so that slab is about 1.23 cu yd before waste.
Bags vs ready-mix
An 80 lb bag of premixed concrete yields about 0.6 cubic feet; a 60 lb bag, about 0.45. That slab needs roughly 56 of the 80 lb bags — which is why anything past about half a cubic yard is usually cheaper and far easier ordered as ready-mix from a truck. Bags make sense for post holes, small pads and repairs. Always round up and keep the waste allowance; a short pour is a ruined pour.
This is an estimate, not a structural design
These figures are for planning quantities on small projects. Anything structural — footings that carry a building, reinforced slabs, retaining walls — needs a design from a licensed engineer, who specifies the mix strength (psi), reinforcement and thickness. Don't size structure by estimate; safety depends on the professional calculation.
Reference estimate — not an engineering design. Incorrect sizing can create safety hazards: fire, electric shock or structural failure. Before building, have it validated by a licensed professional (engineer or electrician) and follow the applicable technical standards.
Frequently asked questions
Sources
- Bag yield figures — standard premixed concrete (60/80 lb)
- American Concrete Institute (ACI) — concrete basics
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