Concrete Calculator
Pick the shape you're pouring at the top, enter its dimensions, and get the concrete volume in cubic yards and cubic feet, the number of pre-mix bags in your chosen size, and an optional cost estimate. Slab covers slabs, patios, driveways, footings and walls; round handles columns, piers and Sonotube forms (and round pads); stairs figures a solid poured flight of steps. Add a waste allowance under advanced options if you want to buy a little extra — it's off by default so the headline is the exact volume.
Your measurements
Slab = slabs, patios, driveways, footings and walls. Round = columns, piers, Sonotube forms and round pads. Stairs = a solid poured flight of steps.
4 in is standard for patios and walkways; 5–6 in for driveways. For a footing or wall, this is its depth/height.
How many identical pours you're doing.
Pick the bag you're buying. Switch any time to compare counts.
Concrete needed
1.48 yd³
≈ 67 × 80 lb bags
Bags needed by bag size
Typical installed cost
Installed, materials + labor — a ballpark to sanity-check bids, not a quote. See the cost breakdown.
Estimates only. Verify against your supplier's coverage figures before ordering.
Footprint
Footprint to scale
Coverage
- Surface area
- 120 ft²(length × width)
The formula
Slab: yd³ = L ft × W ft × (thickness in ÷ 12) ÷ 27 · Round: yd³ = π × (diameter in ÷ 24)² × height ft ÷ 27 · Stairs: yd³ = width ft × run ft × rise ft × [n(n+1)/2] ÷ 27 — each × quantity × (1 + waste %)
Example: A 10 ft × 12 ft patio at 4 in thick = 40 ft³ → 1.48 yd³ (~67 × 80 lb bags). A 12 in round column 4 ft tall = 3.14 ft³ → 0.12 yd³ (~6 × 80 lb bags). A 4-step flight at 7 in rise, 11 in run, 3 ft wide = ~16 ft³ → 0.59 yd³ (~27 bags).
How it works
- 1Pick the shape you're pouring — slab (rectangular), round (a column, pier, tube or round pad), or stairs.
- 2For a slab: length × width × thickness (thickness ÷ 12 to convert inches to feet) gives cubic feet.
- 3For a round shape: π × radius² × height — a column, footing and round pad are all cylinders, so the same formula covers them.
- 4For stairs: a solid flight is width × run × rise × [1 + 2 + … + n] for n steps — each step back adds another layer of concrete.
- 5Multiply by the quantity, divide cubic feet by 27 for cubic yards, then divide by the bag yield (0.45 ft³ for 60 lb, 0.6 ft³ for 80 lb) — or order ready-mix by the yard past ~1 yd³.
Frequently asked questions
How many 80 lb bags of concrete make a cubic yard?
An 80 lb bag yields about 0.6 ft³ of mixed concrete, and a cubic yard is 27 ft³, so you need 27 ÷ 0.6 = 45 bags per cubic yard.
How thick should a concrete slab be?
4 inches is standard for patios, sidewalks and shed floors. Use 5–6 inches for driveways and anywhere vehicles or heavy loads sit.
How much concrete do I need for a Sonotube or round column?
Switch the shape to Round column and enter the tube diameter and height. A column is a cylinder, so the volume is π × (diameter ÷ 2)² × height. A 12-inch tube 4 ft tall holds about 3.14 cubic feet — roughly 6 × 80 lb bags or 0.12 cubic yards.
How do you calculate concrete for stairs?
Switch the shape to Stairs and enter the number of steps, the rise and run, and the width. A solid flight is width × run × rise × [1 + 2 + … + n], because each step further back sits on another layer of concrete. A 4-step flight at 7 in rise, 11 in run and 3 ft wide is about 16 cubic feet — roughly 0.6 cubic yards or 27 × 80 lb bags.
Should I order ready-mix or use bags?
Bags are practical up to roughly 1 cubic yard (about 45 × 80 lb bags). Beyond that, ordering ready-mix delivered by truck is usually cheaper and far less labor.