Concrete Calculator
Cubic yards of concrete for slabs, footings, round columns and stairs, plus 60-lb and 80-lb bag counts (Quikrete yields), weight and cost — with the math shown.
Concrete Calculator: with the default inputs, concrete needed is 1.23 yd³.
Column and stair dimensions are under More options.
Identical slabs, footings, columns or stair runs.
Slab length, or the total run of a footing trench.
4 in is standard for patios and walkways; 5–6 in for driveways.
Net volume of the pour, before waste.
- Order with waste
- 1.36 yd³Net volume plus your waste percentage — what to order.
- Cubic feet
- 33.33
- 60-lb bags
- 82Each yields about 0.45 ft³; includes waste.
- 80-lb bags
- 62Each yields about 0.60 ft³; includes waste.
- Weight of concrete
- 4,994 lbAt about 150 lb per cubic foot.
- Ready-mix cost
- $0.00
- Cost in 80-lb bags
- $0.00
Assumptions
- Bag yields use Quikrete's published figures (0.30 / 0.45 / 0.60 ft³ for 40 / 60 / 80-lb bags); other brands are within a few percent.
- Weight uses 150 lb/ft³ (2,400 kg/m³), typical for normal-weight concrete.
- Stairs are modeled as solid steps on grade; formed stairs with a hollow underside use less.
| Bag | Yield (ft³) | Bags per yd³ | Bags for this job |
|---|---|---|---|
| 40 lb | 0.3 | 90 | 123 |
| 60 lb | 0.45 | 60 | 82 |
| 80 lb | 0.6 | 45 | 62 |
Yields are approximate and include the water you add. Counts include your waste percentage.
| Thickness (in) | Order with waste (yd³) | 80-lb bags | Ready-mix cost |
|---|---|---|---|
| 3 | 1.02 | 46 | $0.00 |
| 3.5 | 1.19 | 54 | $0.00 |
| 4 | 1.36 | 62 | $0.00 |
| 5 | 1.7 | 77 | $0.00 |
| 6 | 2.04 | 92 | $0.00 |
| 8 | 2.72 | 123 | $0.00 |
4 in is standard for patios and walkways, 5–6 in for driveways and anything a vehicle parks on, 3½ in only for footpaths that will never see a wheel. Figures include your waste percentage; the cost column is blank until you enter a ready-mix price.
How this is worked out
The formula
Slab / footing: V = length × width × thickness Round column: V = π × (diameter ÷ 2)² × height Stairs: V = width × rise × (run × n(n+1)/2 + n × landing depth), n = number of steps Cubic yards = cubic feet ÷ 27 80-lb bags = cubic feet ÷ 0.60 60-lb bags = cubic feet ÷ 0.45 Weight ≈ cubic feet × 150 lb
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Shape
- Column and stair dimensions are under More options.Slab, pad or wall (length × width × thickness) · Footing or trench (length × width × depth) · Round column / sonotube (More options) · Stairs (More options)
- How many
- Identical slabs, footings, columns or stair runs.from 1 to 10000 · whole numbers only · defaults to 1
- Length
- Slab length, or the total run of a footing trench.in ft, in, yd, m, cm · 0 or more · defaults to 10
- Width
- A number.in ft, in, yd, m, cm · 0 or more · defaults to 10
- Thickness / depth
- 4 in is standard for patios and walkways; 5–6 in for driveways.in in, ft, cm, mm, m · 0 or more · defaults to 4
- Column diameter(under More options)
- Sonotube inside diameter, e.g. 8, 10 or 12 in.in in, ft, cm, mm, m · 0 or more · defaults to 12
- Column height(under More options)
- A number.in ft, in, m, cm · 0 or more · defaults to 4
- Number of steps(under More options)
- A number.from 1 to 100 · whole numbers only · defaults to 4
- Rise per step(under More options)
- A number.in in, cm, mm · 0 or more · defaults to 7
- Run (tread depth)(under More options)
- A number.in in, cm, mm · 0 or more · defaults to 11
- Stair width(under More options)
- A number.in ft, in, m, cm · 0 or more · defaults to 4
- Top landing depth(under More options)
- Extra depth of the top step if it doubles as a landing. Leave 0 if not.in in, ft, cm, m · 0 or more · defaults to 0
- Waste / overage(under More options)
- Uneven subgrade, spillage and form bulge eat 5–10%. Bag counts and cost include this.a percentage · from 0 to 100 · defaults to 10
- Ready-mix price per cubic yard(under More options)
- Delivered price from your local plant; leave 0 to skip.in dollars · 0 or more · defaults to 0
- Price per 80-lb bag(under More options)
- A number.in dollars · 0 or more · defaults to 0
What you get back
- Concrete neededmain answer
- Net volume of the pour, before waste.
- Order with waste
- Net volume plus your waste percentage — what to order.
- Cubic feet
- 60-lb bags
- Each yields about 0.45 ft³; includes waste.
- 80-lb bags
- Each yields about 0.60 ft³; includes waste.
- Weight of concrete
- At about 150 lb per cubic foot.
- Ready-mix cost
- Cost in 80-lb bags
What this assumes
- Bag yields use Quikrete's published figures (0.30 / 0.45 / 0.60 ft³ for 40 / 60 / 80-lb bags); other brands are within a few percent.
- Weight uses 150 lb/ft³ (2,400 kg/m³), typical for normal-weight concrete.
- Stairs are modeled as solid steps on grade; formed stairs with a hollow underside use less.
About this calculator
Concrete is sold by the cubic yard when it comes on a truck and by the bag when you mix it yourself, so the first job is turning your dimensions into cubic feet and yards. Pick the shape, enter the dimensions in whatever units you measured, and you get the net volume, the volume to order with waste, and how many 60-lb or 80-lb bags that is.
Getting the measurements right
- Slabs and pads: measure the inside of the forms, not the outside. Thickness is the number people get wrong — a "4-inch" slab poured over a rough gravel base often averages 4½ in, which is 12% more concrete. Measure at several points and use the average.
- Footings: use the trench length, trench width and the depth you'll fill to. If the trench walls slough, add more waste.
- Sonotubes and piers: use the tube's inside diameter. A 12-in tube 4 ft tall is about 3.1 ft³, so a bag calculation matters more than you'd think — that's five or six 80-lb bags per pier.
- Stairs: the calculator assumes solid stairs poured on grade, where each step is a full-width block that runs back to the rear of the pour. That's the conservative (and usual) way to form them.
Bags versus a truck
An 80-lb bag of Quikrete Concrete Mix yields about 0.60 ft³; a 60-lb bag about 0.45 ft³. A single cubic yard is 45 bags — 3,600 lb of material to haul, mix and place before the first batch stiffens. Rule of thumb from the field: under about half a yard, bags make sense; over a yard, order ready-mix even with a short-load fee. Between the two, it depends on access and how many strong backs you have.
Why the waste factor matters
Ten percent is the standard allowance. It covers an uneven subgrade, spillage from the chute or wheelbarrow, form bulge and the last bit stuck in the drum. Running out mid-pour means a cold joint, so if you're on the fence between two truck sizes, round up.
Reading the results
The primary number is the net volume of the shape; Order with waste is what you actually tell the dispatcher. Bag counts already include waste and are rounded up to whole bags. Weight uses 150 lb/ft³ (normal-weight concrete), which is useful for checking what a trailer or deck can hold.
Frequently asked questions
▸How many 80-lb bags of concrete make a cubic yard?
About 45. An 80-lb bag yields roughly 0.60 ft³ and a cubic yard is 27 ft³. For 60-lb bags it's 60, and for 40-lb bags 90.
▸How much concrete do I need for a 10×10 slab?
At 4 in thick, 10 × 10 × (4 ÷ 12) = 33.3 ft³, which is 1.23 cubic yards — or about 62 80-lb bags once you add 10% waste.
▸How thick should a concrete slab be?
4 in for patios, sidewalks and shed floors; 5–6 in for residential driveways; 6 in or more where trucks or RVs will park. Thicker slabs also need proper base preparation and reinforcement to perform.
▸Should I add extra when ordering ready-mix?
Yes — 5–10% is normal. Running short means a second truck with another delivery charge, or a cold joint in your slab. Most plants sell in quarter-yard increments, so round up to the next quarter.
▸How much does a cubic yard of concrete weigh?
Roughly 4,050 lb (about 2 US tons) for normal-weight concrete at 150 lb/ft³. Wet concrete weighs about the same as cured.
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