Gardening & Plants
Concrete Volume Calculator
Calculate cubic yards of concrete needed for a slab, footing, or path.
Concrete is sold in cubic yards for ready-mix trucks and bags for smaller projects. Under-ordering means a visible joint; over-ordering wastes money. This calculator ensures you order exactly the right amount.
Concrete Needed
1.23 cu yards
- with Waste
- 1.36 cu yards (10% waste)
- bags80lb
- 56 bags (80 lb bags, 0.6 cu ft each)
- slab Area
- 100 sq ft
Formula and method
Volume = L × W × (Thickness/12); Yards = Volume / 27
Standard concrete volume formula. 10% waste recommended for forms and spillage. 80-lb bag covers approximately 0.6 cubic feet.
Worked examples
Garden shed pad 10×10
- Length (ft):
- 10
- Width (ft):
- 10
- Thickness (inches):
- 4
Concrete Needed: 1.23 cu yards
Driveway section
- Length (ft):
- 20
- Width (ft):
- 10
- Thickness (inches):
- 6
Concrete Needed: 3.70 cu yards
Assumptions and limits
- 10% waste factor for ready-mix
- Rectangle shape
- 80-lb bag = 0.6 cu ft
This tool provides an educational estimate. Rules, rates and personal circumstances can change the answer. Review the assumptions before relying on a result. Report a correction.
Common mistakes to avoid
- Not ordering 10% extra — a cold joint (re-pour seam) where concrete was added after hardening is a structural weakness.
- Forgetting to account for reinforcing bar displacement when pouring around rebar.
- Ordering bagged concrete for large pours — mixing bagged concrete for anything over 1 cubic yard is extremely labor intensive.
Frequently asked questions
Should I order ready-mix or use bags?
Ready-mix trucks deliver a minimum of about 0.5-1 cubic yards. For anything under 0.5 yards, bagged concrete is more economical. A standard 10×10×4" slab (1.23 cu yards) is at the borderline where ready-mix often makes sense.