Concrete Calculator (Cubic Yards / Meters)
Calculate concrete volume for slabs, footings, columns, and pads in cubic yards and cubic meters, with bag-mix equivalents.
What this calculates
Concrete is sold by volume — cubic yards in the US, cubic meters elsewhere. Underestimating is expensive because half-loads cost more per yard and a return trip means stitching joints into wet pour. This calculator estimates the volume for a slab and shows the bag-mix equivalent for small jobs.
Formula & how it works
Volume (cubic feet) = length × width × thickness (all in feet). Convert: ÷27 for cubic yards, ÷35.31 for cubic meters. Bag mix: 60 lb bag yields ~0.45 cu ft; 80 lb bag yields ~0.60 cu ft. Add 10 % waste for forms and uneven ground.
Worked example
10 × 12 ft patio, 4 inches (0.33 ft) thick. Volume = 10 × 12 × 0.33 = 40 cu ft = 1.48 cu yd. Add 10 % → order 1.7 cu yd ≈ 1.75 yards (typical truck delivery minimum). In 80 lb bags: 40 ÷ 0.6 = 67 bags — clearly worth a truck delivery.
Frequently asked questions
What thickness for a driveway?
Minimum 4 inches for passenger vehicles. 5–6 inches for trucks or RVs. 6 inches with rebar for cold climates with freeze/thaw cycles.
How much waste should I add?
10 % typical for slabs on level ground. 15 % for irregular shapes or rough excavation. Some local pours need more for over-dig at edges.
When are bag mixes better?
Small jobs: footings, fence posts, small pads under 100 sq ft. Above that, a truck delivery is cheaper and easier than mixing dozens of bags by hand.
Do I need rebar?
Most slabs over 4 inches benefit from rebar or wire mesh. Driveways and patios in freezing climates definitely need it. Sidewalks and small pads can often skip it.