Concrete Calculator
Work out the concrete for slabs, round slabs, footings, walls, columns, tubes, steps and curbs: cubic yards or m³ with waste, 40/50/60/80 lb premix bags, ready-mix order, weight and cost.
How it works
slab = length × width × thickness · round slab = π ÷ 4 × diameter² × thickness · footing = length × width × depth · column = π ÷ 4 × diameter² × height · tube = π ÷ 4 × (outside² − inside²) × height · steps = width × rise × (run × n(n−1)/2 + n × landing) · curb and gutter = length × (curb depth × (curb height + flag thickness) + gutter width × flag thickness) · cubic yards = cubic feet ÷ 27 · order = volume × (1 + waste%) · bags = order ÷ bag yield (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 50 lb ≈ 0.375, 40 lb ≈ 0.30), rounded up
Pick what you are pouring and enter its size; inches are divided by 12 to get feet, so every shape comes out in cubic feet, then ÷ 27 gives cubic yards (27 cu ft per yard). Round shapes use π ÷ 4 × diameter². Steps are stacked blocks: each step is as deep as its tread and as tall as all the rises below it, with the top landing usually deeper than a tread. The waste allowance covers spillage, form bulges and uneven subgrade — running short mid-pour leaves a cold joint, so 5–10% extra is normal. Premix bag counts use typical yields for standard concrete mix (an 80 lb bag makes about 0.60 cu ft) and include the waste. Ready-mix is ordered in quarter-yard steps, so the order is rounded up; a truck carries about 10 cubic yards. Add your local bag and ready-mix prices to see which is cheaper — bags usually win below about one cubic yard. Weight assumes about 150 lb per cubic foot (2,400 kg/m³) of cured concrete.
Worked example
A 10 × 10 ft slab at 4 in: 10 × 10 × (4 ÷ 12) = 33.33 cu ft, ÷ 27 = 1.23 cubic yards. With 10% extra the order is 1.36 cu yd (36.67 cu ft), which is 62 eighty-pound bags or 82 sixty-pound bags. Ready-mix rounds up to 1.50 cu yd; at $165 per yard that is $247.50 against $403 for 62 bags at $6.50 — so for this slab the truck is cheaper and far less work. Three steps 4 ft wide with 7 in rises, 11 in treads and a 36 in landing need 4 × (7/12) × [(11/12) × 3 + 3 × 3] = 27.4 cu ft, about 1.02 cu yd.
Sources: QUIKRETE Concrete Mix product data (bag yields) · NIST Handbook 44, Appendix C (cubic yard and cubic foot)
Frequently asked questions
How much extra concrete should I order?
Add 5–10%, or more over rough or sloping ground. Subgrade dips, spillage and slightly bowed forms all eat into the pour, and running short mid-pour risks a cold joint. Ready-mix suppliers sell in quarter-yard steps, so the calculator rounds the truck order up for you.
How many bags of concrete make a cubic yard?
About 45 eighty-pound bags, 60 sixty-pound bags, 72 fifty-pound bags or 90 forty-pound bags, based on typical yields of 0.60, 0.45, 0.375 and 0.30 cu ft per bag. Check your brand’s label — yields vary slightly between mixes.
When are bags cheaper than ready-mix?
Bags usually win for post holes, footings and pads under roughly ½ to 1 cubic yard. Above that, mixing 40-plus bags by hand is slow and uneven, and ready-mix plus any short-load fee is often cheaper. Enter both prices under More options to compare for your job.
What thickness does a slab need?
Four inches is standard for patios, walkways and shed floors; go to 5–6 in for driveways and anything carrying vehicles. Local code and soil conditions set the real minimum, so confirm before you pour.
How do I calculate concrete for steps?
Choose Steps and enter the width, the rise and run of each step, the number of steps (including the top landing) and the landing depth. Each step is treated as a block as tall as all the rises beneath it, which is how competitors and contractors estimate solid steps.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.