Concrete Calculator
Cubic yards and bags for slabs, footings, and columns.
Pours
One row per pour — a slab, a run of footings, a set of piers. Measure in feet and inches; slab thickness and footing depth are entered in inches. Your inputs are saved on this device automatically.
Slab / wall — 33.33 ft³ · 1.23 yd³
Column / pier — 12.57 ft³ · 0.47 yd³
How much concrete
Bags of pre-mixed concrete
Whole bags to cover the volume to order, at the typical manufacturer yield printed on the bag. Partial bags round up.
| Pour | Dimensions | Qty | ft³ | yd³ |
|---|---|---|---|---|
| Slab / wall | 10′ × 10′ × 4″ | ×1 | 33.33 | 1.23 |
| Column / pier | 12″ ⌀ × 4′ | ×4 | 12.57 | 0.47 |
| Waste allowance (10%) | 4.59 | 0.17 | ||
| To order | 50.49 | 1.87 |
Cost — optional, at your own prices
Concrete pricing is local and moves, so nothing is filled in for you. Type the price your plant or yard quotes and the volume above is priced at it. Delivery, short-load fees, and pumping are separate lines on the plant’s ticket.
How it works
Concrete is ordered by the cubic yard, and one cubic yard is 27 cubic feet of placed concrete. Figure each pour's volume — length × width × thickness for a slab, footing, or wall; π × radius² × height for a round column or pier — total them, then add a waste allowance for spillage and uneven subgrade. To buy bags instead of ready-mix, divide the cubic feet by the yield printed on the bag: typically 0.60 cubic feet for an 80 lb bag, 0.45 for a 60 lb, and 0.30 for a 40 lb — 45, 60, or 90 bags per cubic yard.
Add a row for each pour
Pick the shape: a slab or wall (rectangular), a footing or trench, or a round column or pier. A real job is usually several rows — a slab plus a run of footings plus a set of piers — and they all ride on the same truck.
Measure in feet and inches
Enter length and width in feet plus inches, and slab thickness or footing depth in inches. For a round pour, enter the tube's diameter in inches and its height. Set how many identical pours that row covers and the count is carried through the volume.
Add a waste allowance
Concrete is lost to spillage, over-dig, and a subgrade that is never perfectly flat, and a short pour is far worse than a leftover wheelbarrow. 10% is a common allowance; go higher over rough or hand-dug ground.
Read the yards and the bag counts
The results show net volume, the volume to order with waste, and whole bags of 40, 60, and 80 lb pre-mixed concrete for that volume. Type the price your plant or store quotes and the same volume is priced at it — no prices are filled in for you.
Frequently asked questions
- How much concrete do I need?
- Work in cubic feet, then convert. For a slab, footing, or wall: length (ft) × width (ft) × thickness (ft) — divide inches by 12 to get feet. For a round column or pier: π × (diameter ÷ 2)² × height. Add up every pour, divide the total by 27 for cubic yards, and add a waste allowance on top.
- How many 80 lb bags of concrete are in a cubic yard?
- 45. An 80 lb bag of pre-mixed concrete yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags. At the same typical yields it takes 60 bags of 60 lb (0.45 cubic feet each) or 90 bags of 40 lb (0.30 cubic feet each). Yields are what manufacturers print on the bag and vary a little with how wet the mix is worked — check your bag.
- How much extra concrete should I order for waste?
- 10% is a common allowance for spillage, over-dig, and an uneven subgrade. Add more when the ground is rough or hand-dug, or when the forms are deep enough that a small depth error moves real volume. Running short mid-pour means a cold joint and a second delivery, so the allowance is cheap insurance.
- How thick should a concrete slab be?
- Patios, walkways, and shed floors are commonly poured 4 inches thick; driveways and slabs that carry vehicles or heavy equipment are commonly 5 to 6 inches. Those are rules of thumb, not requirements — thickness, reinforcement, and the base under the slab are set by your local building code and by an engineer on anything structural.
- Should I order ready-mix or mix bags myself?
- Bagged mix gets impractical quickly: one cubic yard is 45 eighty-pound bags, about 3,600 lb to haul, open, and mix. Bags suit small pours — setting posts, a pad, a few piers. Beyond roughly half a yard, price the pour with a ready-mix plant. Plants commonly set a minimum load and add a short-load fee under it, so ask what theirs is when you call.
- How do I measure footings and round piers?
- Measure a footing the way you dug it: the trench's length, its width, and its depth — the same length × width × depth math as a slab. For a round pier, the diameter of the form tube is the measurement that matters, not the hole you augered. Enter one row with the pier's diameter and height and set the count to the number of piers.