Concrete Cubic Yard Calculator
How many cubic yards of concrete do you need? Enter slab or round dimensions and thickness, and this cubic yards of concrete calculator gives the yardage to order — with a 10% waste factor — plus 60-lb and 80-lb bag counts for small pours.
Order quantity includes 10% waste. Bag counts use exact yardage (no waste).
Estimates only — not financial advice. This calculator gives approximate figures for planning. It is not financial, tax, or legal advice; check with a qualified professional before making decisions.
How the concrete cubic yard calculator works
Ready-mix concrete sells by the cubic yard (27 cubic feet). Multiply length × width × thickness in feet to get cubic feet, then divide by 27 for yards. For a round pad, the area is π × radius² before the same thickness step.
The order quantity adds 10% waste because subgrade is never perfectly level — forms spill, wheelbarrows slop, and thin spots need topping up. For bag mixes, the counts divide the exact cubic feet by each bag’s yield (0.45 cu ft for 60-lb, 0.6 for 80-lb) and round up.
cu yd = L × W × (T/12) / 27 · round: area = π × (d/2)² · order = cu yd × 1.1
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Concrete cubic yard calculator FAQ
How many cubic yards of concrete do I need?
Multiply length × width × thickness (in feet) and divide by 27. A 20 × 10 ft slab at 4 inches thick is 20 × 10 × (4/12) ÷ 27 ≈ 2.47 cubic yards — order about 2.7 with waste.
What is the formula for cubic yards of concrete?
Cubic yards = (length in ft × width in ft × thickness in ft) ÷ 27. For round pads, replace length × width with π × (diameter/2)².
What waste factor should I use for concrete?
10% is standard for slabs and footings — subgrade irregularities always eat concrete. Use 15% for rough, hand-dug footings or uneven ground.
Bags or ready-mix: which is cheaper?
Bags win under about 1 cubic yard (roughly 45 sixty-lb bags); above that, a ready-mix truck is cheaper per yard and far less labor. Bag counts above are for the exact yardage with no waste.
How thick should a concrete driveway be?
4 inches is the minimum for passenger cars; 5–6 inches for heavy trucks and RVs. Every extra inch of thickness adds 25% more concrete to a 4-inch slab’s volume.