Concrete Calculator
Pick your shape, enter the measurements, and get cubic yards for a ready-mix order or a bag count for the truck bed. The formula is shown with the result.
Past about one cubic yard (roughly 45 × 80-lb bags), mixing by hand stops being fun and starts being a shoulder injury — that's where ready-mix delivery earns its minimum-load fee. Under half a yard, bags win. In between, it's your call and your Saturday.
How this is calculated
Slab: length × width × (thickness ÷ 12) = cubic feet. Footing: length × (width ÷ 12) × (depth ÷ 12). Column: π × radius² × height, radius in feet, times the count.
Divide cubic feet by 27 for cubic yards. Bag counts use the standard yields: an 80-lb bag makes about 0.60 cubic feet, 60-lb about 0.45, 40-lb about 0.30 — then round up, always.
Common questions
How many bags make a cubic yard?
About 45 of the 80-lb bags, 60 of the 60-lb, or 90 of the 40-lb. Seeing those numbers is usually the moment people call the ready-mix plant.
How thick should my slab be?
Common practice: 4 inches for patios and walkways, more for driveways and anything holding vehicles. Thickness and any required reinforcement are code and load questions — check your local building department before you pour, not after.
Does rebar or mesh change how much concrete I need?
Not meaningfully — reinforcement displaces a negligible volume. Figure the full pour volume regardless.
What if I come up short mid-pour?
That's the one failure to really avoid: a pour that sets in two batches makes a weak seam (a cold joint). It's why every answer on this page says round up — extra bags return; a cold joint doesn't.
Part of MeasureTwiceMath — free construction and DIY calculators. Quantities only, not structural advice; footing and slab requirements are set by your local code. Related: cubic yard calculator · square footage calculator.