Cubic Yards: The standard ordering unit for concrete. Ready-mix trucks deliver in cubic yards; a typical truck holds 8–10.
Cubic Feet: Useful for small pours where you're counting bags rather than ordering a truck.
Bag Counts (40/60/80 lb): How many pre-mixed bags of each weight you'd need to buy from a home center. Larger bags cost less per cubic foot but are heavier to lift.
Cubic Meters: The volume in metric units, handy for international specifications or engineering plans.
How This Calculator Works
You enter the slab's length and width in feet and its thickness in inches. The tool converts thickness to feet, then multiplies all three dimensions for cubic feet. It divides by 27 for cubic yards and by 35.3147 for cubic meters. Bag counts use the standard yields: one 80 lb bag covers about 0.6 cubic feet, one 60 lb bag about 0.45, and one 40 lb bag about 0.3.
Quick Questions
Should I order extra concrete?
Yes. Plan for 5–10% extra to account for spillage, uneven sub-grade, and forms that aren't perfectly level.
When should I use bags vs. a ready-mix truck?
Bags are practical for projects under about 1 cubic yard. Above that, ordering a ready-mix truck is generally faster and more cost-effective.
How thick should a concrete slab be?
Sidewalks typically use 4 inches, driveways 4–6 inches, and garage floors 6 inches. Check local building codes for requirements.
Does this calculator include reinforcement?
No. Wire mesh or rebar is figured separately and depends on the slab's intended load.
What's the difference between cubic feet and cubic yards?
One cubic yard equals 27 cubic feet. Contractors and suppliers almost always quote concrete in cubic yards.