Cubic yards, bag counts and ready-mix cost. Add every pour on the job to one list and get a single order figure.
Every pour you add shows up here. The total is what you order.
| Pour | Dimensions | Cu yd | |
|---|---|---|---|
| Nothing added yet. | |||
Slab, footing and wall: length × width × thickness, converted to cubic feet, divided by 27 to get cubic yards.
Round column: π × radius² × height.
Stairs: treated as a stack of rectangular slabs — the bottom step runs the full depth, each step above it one run shorter. Volume = width × run × rise × (N × (N+1) ÷ 2), where N is the number of steps. An optional landing is added on top.
Bag yields are the manufacturer standards: an 80 lb bag of mixed concrete yields about 0.60 cu ft, a 60 lb bag about 0.45, a 40 lb bag about 0.30. Bag counts are rounded up — you cannot buy three-fifths of a bag.
Waste is applied to the finished volume. 10% is a sensible default for a formed pour on flat ground; go to 15% or more for uneven subgrade, hand-dug footings, or anything you cannot screed flat.
Rough rule: under about half a cubic yard, bags are fine. Half a yard is roughly 23 × 80 lb bags — around 1,840 lb of material to carry, mix and place before it sets. Past that, mixing by hand stops being economical and starts being a cold joint waiting to happen. Above a yard, call the supplier.
Multiply length by width by thickness, all in feet, then divide by 27. A 20 by 12 ft slab at 4 inches thick is 20 x 12 x 0.333 = 80 cubic feet, which is 2.96 cubic yards. Add 10% for waste and you are ordering 3.26. The calculator above does this for you and handles footings, columns, walls and stairs too.
Forty-five. An 80 lb bag of mixed concrete yields about 0.60 cubic feet, and there are 27 cubic feet in a yard. A 60 lb bag yields about 0.45 cubic feet, so you need 60 of those, and a 40 lb bag yields about 0.30, so you need 90.
Rough rule: under about half a cubic yard, bags are fine. Half a yard is roughly 23 x 80 lb bags — around 1,840 lb of material to carry, mix and place before it starts setting. Past that, mixing by hand stops being economical and starts being a cold joint waiting to happen. Above a yard, call the supplier.
10% is a sensible default for a formed pour on flat ground, which is what this calculator uses. Go to 15% or more for uneven subgrade, hand-dug footings, or anything you cannot screed flat. Running out mid-pour costs far more than over-ordering does.
A standard mixer holds about 10 cubic yards. Most suppliers also charge a short-load fee under roughly 4 to 5 yards, so a small pour can carry a surcharge. The calculator has a short-load minimum field so you can price that in.
Treat the stairs as a stack of rectangular slabs: the bottom step runs the full depth, each step above it one run shorter. Volume = width x run x rise x (N x (N+1) / 2), where N is the number of steps. The stairs tab above runs that formula and lets you add a landing on top.