Concrete Calculator
Concrete is ordered in cubic yards but planned in feet and inches, and the arithmetic between them is where budgets leak: a 10 × 10 ft patio at 4 inches deep is 33.3 cubic feet, which is 1.23 cubic yards — order one yard and you are short, order two and you paid for a third of a truck you didn't need. Enter the slab's length, width and thickness and this calculator converts straight to yards, with the 80 lb and 60 lb bag counts for the small-job alternative.
The note carries the two rules that separate a clean pour from a cold joint: add 5-10% for spillage and uneven subgrade, and cross the bags-versus-truck threshold honestly — below roughly a cubic yard, mixing bags makes sense; above it, ready-mix wins on both cost and consistency. Metric mode computes in cubic meters with the yard equivalent alongside. Your slab numbers stay on this device for the next stage of planning.
How to use
- Enter the slab length and width, then pick the thickness - 4 in for patios, 6 in for driveways.
- Read cubic yards for the ready-mix order and bag counts for small jobs.
- Add 5-10% waste per the note, then share or bookmark - dimensions are remembered.
Frequently asked questions
How many bags of concrete per cubic yard?
A cubic yard is 27 cubic feet, and an 80 lb bag yields about 0.60 cubic feet - so 45 bags per yard. Sixty-pound bags yield 0.45 cubic feet, needing 60 per yard. The calculator shows exact counts for your volume; just add the 10% waste margin before checkout.
How much concrete for a 10x10 slab?
It depends entirely on thickness: 4 inches deep is 1.23 cubic yards, 6 inches is 1.85. This is why thickness is a dropdown rather than an afterthought - the difference between patio spec and driveway spec is half a truck.
Should I order extra concrete?
Yes - 5-10% covers spillage, uneven subgrade, and the edge of the form that always seems deeper than measured. Coming up short mid-pour means a cold joint and a weakened slab, which costs far more than the extra quarter yard.
Bags or ready-mix truck - which is cheaper?
Below about one cubic yard, bags win once you factor the short-load fees trucks charge for small pours. Above a yard, ready-mix wins decisively on labor and consistency - hand-mixing 45 bags is a full, miserable day, and the result is only as uniform as your mixing.