Concrete Calculator
Cubic yards and cubic feet for slabs, footings, walls, round piers, stairs and curb and gutter — with a bag count from the yield on your bag, not a guessed constant. How it works
Concrete needed
cubic yards
- Cubic feet
- 48cu ft
- Cubic metres
- 1.36m³
- Bags
- bags
Ready-mix is sold by the cubic yard. Ask your supplier about the minimum load and the ordering increment before you round.
Show the calculationHide the calculation3 steps
The working
Area = Length × Width
= 12 ft × 12 ft
= 144 ft²
Volume = Area × Thickness
= 144 ft² × 0.333 ft
= 48 cu ft
Cubic yards = Cubic feet ÷ 27
= 48 ÷ 27
= 1.78 cu yd
Choose what you are pouring — slab, footing, wall, round pier, stairs or curb and gutter — and enter its dimensions. The calculator gives the volume in cubic yards, cubic feet and cubic metres, adds the overage you choose, and turns it into whole bags once you enter the yield printed on the bag. It does not pick a thickness for you and it does not price the concrete — those come from your plan and your supplier.
How this calculator works
Only your inputs and exact unit conversions. Where a figure comes from anywhere else, it is recorded below with its source.
- Formula version
- 1.2.1
- Last reviewed
- 2026-09-29
- External data
- 3 sources
- Category
- Materials
What this calculates
The volume of concrete a shape needs, in cubic yards because that is how ready-mix is sold, and in cubic feet because that is how bagged mix is labelled. Slabs, footings and walls are rectangular prisms; piers and tubes are cylinders; stairs and a curb and gutter are built up from rectangles. Everything is exact geometry.
The arithmetic
A slab is length × width × thickness. A footing is the same with its own width and depth, because they are usually in inches while the run is in feet. A wall is length × height × thickness. A round pier or tube form is π × diameter² ÷ 4 × height; per foot of height that is π × d² ÷ 576 cubic feet with d in inches, the basis of the table by diameter below. The result is in cubic feet; dividing by 27 gives cubic yards.
Stairs are poured solid to the ground, so step k is a block k rises tall. Together the steps are width × run × rise × (1 + 2 + … + n), and an optional landing at the top adds width × depth × the total rise. A curb and gutter is a cross-section times its length: curb thickness × curb height, measured above the gutter, plus gutter width × gutter thickness, where the gutter runs under the curb so nothing is counted twice.
The thickness is entered in inches and converted, so 4 inches is 0.333 feet in the working — the mistake this catches is multiplying feet by inches and getting a number twelve times too big.
Bags
A bag of concrete mix yields a fixed volume once mixed, and that volume is printed on the bag and stated in the manufacturer’s data sheet. It changes with the product and with the bag weight. The calculator divides your cubic feet by that yield and rounds up to whole bags — it never ships a "bags per yard" constant, because there is no such number without knowing which bag.
For one product the data-sheet figures are built in as labelled options: QUIKRETE Concrete Mix No. 1101, whose sheet states 0.30, 0.375, 0.45, 0.60 and 0.675 cubic feet for the 40, 50, 60, 80 and 90 lb bags, and calls each figure approximate. The source is recorded in full below. Any other product: enter the yield from its bag.
Overage
Real subgrades are not flat, forms bow, and some concrete stays in the chute. The overage field adds a percentage you choose to the order quantity. It is blank by default: the right allowance depends on how the subgrade was prepared and how the pour is done, and a default would just be a number pretending to be advice.
What it does not decide
Thickness. The tool takes the thickness your plan or your building department gives, and recommends none. What the model codes and some cities and states set is quoted, with section numbers, in the concrete slab thickness guide linked on this page. It also does not price concrete — ready-mix is quoted per yard with delivery, minimum-load and short-load terms that only your supplier knows.
A 12 ft × 12 ft slab, 4 inches thick, with 10% overage
The dimensions, the 4 in thickness and the 10% overage are example inputs, not recommendations.
- Length × width
- 12 ft × 12 ft
- Thickness
- 4 in = 0.333 ft
- Overage
- 10%
- 01Area= 12 × 12= 144 sq ft
- 02Volume= 144 × 0.333= 48 cu ft
- 03Cubic yards= 48 ÷ 27= 1.78 cu yd
- 04Order quantity= 1.78 × 1.10= 1.96 cu yd (52.8 cu ft)
- 05Bags= 52.8 ÷ yield on the bag= rounded up to whole bags
1.78 cu yd — order 1.96 cu yd
Concrete per foot of round form, by diameter
How much concrete each foot of a round pier, column or tube form holds, and how many feet of it one cubic yard fills. Each row is π × diameter² ÷ 4 with the diameter in feet, which is π × d² ÷ 576 cubic feet per foot with d in inches; divide by 27 for cubic yards. Multiply by the height, or use round mode above for any diameter, height and number of forms.
| Diameter | Cu ft per ft of height | Cu yd per ft of height | Ft of tube per cu yd |
|---|---|---|---|
| 6 in | 0.196 | 0.0073 | 137.5 |
| 8 in | 0.349 | 0.0129 | 77.3 |
| 10 in | 0.545 | 0.0202 | 49.5 |
| 12 in | 0.785 | 0.0291 | 34.4 |
| 14 in | 1.069 | 0.0396 | 25.3 |
| 16 in | 1.396 | 0.0517 | 19.3 |
| 18 in | 1.767 | 0.0654 | 15.3 |
| 20 in | 2.182 | 0.0808 | 12.4 |
| 22 in | 2.640 | 0.0978 | 10.2 |
| 24 in | 3.142 | 0.1164 | 8.6 |
| 26 in | 3.687 | 0.1366 | 7.3 |
| 28 in | 4.276 | 0.1584 | 6.3 |
| 30 in | 4.909 | 0.1818 | 5.5 |
| 32 in | 5.585 | 0.2069 | 4.8 |
| 34 in | 6.305 | 0.2335 | 4.3 |
| 36 in | 7.069 | 0.2618 | 3.8 |
| 40 in | 8.727 | 0.3232 | 3.1 |
| 42 in | 9.621 | 0.3563 | 2.8 |
| 48 in | 12.566 | 0.4654 | 2.1 |
| 54 in | 15.904 | 0.5890 | 1.7 |
| 60 in | 19.635 | 0.7272 | 1.4 |
Geometry at the diameter in the first column, with no overage and no footing under the form. Sonoco calls its Sonotube sizes nominal: its Sonotube FAQ says the inside diameter will be “at least the stated diameter, but could be as much as 1" larger” (Sonoco Products Company, Sonotube Frequently Asked Questions, PDF created 2023-03-02, on sonoco.com, read 2026-09-29). For a Sonotube, the cubic-feet and cubic-yard columns are therefore the least that size holds, and the last column the most feet one cubic yard fills. A comparable statement for other brands was not found in the sources reviewed. If it matters, measure the inside and enter that diameter in round mode. The 21 diameters are the rows of the concrete-requirements chart in Sonoco’s Sonotube Commercial brochure (©2016); only the sizes come from it, and every figure here is computed. Sonotube is a registered trademark of Sonoco and QUIK-TUBE a trademark of QUIKRETE; this site is not affiliated with either company.
What it assumes
- 01Uniform thickness across the pour, and vertical form faces.
- 02Round piers are true cylinders of the diameter entered.
- 03Stairs are poured solid to the ground, with a landing solid at the height of the top step.
- 04A curb and gutter has a rectangular cross-section, with the gutter running under the curb.
- 05Overage and bag yield apply only when entered.
- 06Bags are rounded up to whole bags.
What it does not do
- It does not model thickened edges, haunches or a slab that changes depth — split those into parts and add them.
- It does not subtract rebar, mesh or embedded items; their volume is normally negligible.
- Stairs are modelled as solid blocks: a stepped slab over fill, a thickened footing under the stairs and side walls are not, so add them as separate parts. A curb and gutter is the volume of its rectangular section; rounded or sloped faces and the cross-fall of the pan are not modelled.
- It does not recommend a thickness, a mix strength or an overage.
- It does not know your supplier’s minimum load or ordering increment.
- Round mode is the cylinder alone. A wider footing under a pier or tube is not included; work it out in footing or slab mode and add the two.
Common questions.
- How many cubic yards is a 10 × 10 slab at 4 inches?
- 100 sq ft × 0.333 ft = 33.3 cu ft, which is 1.23 cubic yards before any overage. Enter 10, 10 and 4 in slab mode and the working shows each step.
- How many bags of concrete make a cubic yard?
- 27 cubic feet divided by the yield printed on the bag. Different products and bag weights yield different amounts, which is why this calculator asks for the figure instead of assuming one. Enter the yield and it gives whole bags for your pour.
- How many cubic yards is a 10 × 10 slab at 6 inches?
- 100 sq ft × 0.5 ft = 50 cu ft, which is 1.85 cubic yards before any overage. Compare 1.23 cubic yards at 4 inches: a thicker pour needs proportionally more, so check the thickness against your plan before you order.
- How many square feet does a cubic yard of concrete cover?
- It depends on the thickness: 324 divided by the thickness in inches. One cubic yard covers 81 square feet at 4 inches, 64.8 at 5 inches and 54 at 6 inches. That is the quick check behind the working shown in the calculator, and it ignores overage.
- How do I calculate concrete for a footing?
- Pick the footing shape. A footing is length × width × depth, but the width and depth are usually in inches and the run in feet, which is why they have their own fields. A 40 ft run, 16 in wide and 8 in deep is 40 × 1.333 × 0.667 = 35.6 cu ft, or 1.32 cubic yards.
- How much concrete do I need for a wall, a column or a pier?
- A wall is length × height × thickness. A column or pier is the round shape: π × diameter² ÷ 4 × height, times the number of them. Four piers 12 in across and 4 ft deep are 4 × 0.785 × 4 = 12.6 cu ft, or 0.47 cubic yards.
- How much concrete does a 12 in Sonotube or other tube form hold?
- π × diameter² ÷ 4 for each foot of height. A 12 in tube, taken at 12 in across, holds π × 1² ÷ 4 = 0.785 cubic feet per foot: 3.14 cu ft, or 0.116 cubic yards, in a 4 ft length, and one cubic yard fills 34.4 ft of it. An 8 in tube holds 0.349 cu ft per foot, 1.40 cu ft in 4 ft. The table by diameter above runs from 6 to 60 in; round mode takes any diameter, height and number of tubes.
- How many bags of concrete fill a 12 in tube form?
- The tube’s cubic feet divided by the yield printed on the bag, rounded up. With the QUIKRETE Concrete Mix No. 1101 yields built into this calculator, 0.45 cu ft per 60 lb bag and 0.60 per 80 lb bag, a 12 in × 4 ft tube, at exactly 12 in inside, holds π = 3.142 cu ft: 3.142 ÷ 0.45 = 6.98, so 7 sixty-pound bags, or 3.142 ÷ 0.60 = 5.24, so 6 eighty-pound bags. An 8 in × 4 ft tube, at exactly 8 in inside, holds 1.40 cu ft and takes 4 or 3. QUIKRETE’s QUIK-TUBE data sheet gives the same counts. Sonoco says a Sonotube can be up to 1 in wider inside than its stated size (see below), so measure the inside and enter that diameter. Another mix yields a different amount, so enter the figure from your bag.
- Is a 12 in tube form exactly 12 inches across inside?
- Not necessarily. Sonoco calls its Sonotube sizes nominal: its FAQ says the inside diameter is at least the stated size and can be up to 1 in larger. That matters most on small tubes. A 12 in tube that measures 13 in inside holds 169 ÷ 144 = 1.17 times as much, 17% more; an 8 in tube that measures 9 in holds 81 ÷ 64 = 1.27 times as much. A comparable statement for other brands was not found in the sources reviewed. Measure the inside and enter that diameter in round mode.
- How much concrete do I need for stairs?
- Switch to the stairs mode and enter the width, the rise and run of one step, and the number of steps. Each step is poured solid to the ground, so the steps together are width × run × rise × (1 + 2 + … + n). Four steps 4 ft wide, 7 in rise and 11 in run come to 21.4 cu ft, or 0.79 cubic yards; a landing at the top is an extra field. To work out the riser height, the treads and the stringer layout from a total rise first, use the stair calculator, linked under Where people go next.
- How do I calculate concrete for a curb and gutter?
- Multiply the cross-section by the length. The section is the curb thickness × the curb height above the gutter, plus the gutter width × its thickness. A 6 in thick, 6 in high curb on an 18 in wide, 6 in thick gutter is 0.25 + 0.75 = 1.0 sq ft, so 100 ft of it is 100 cu ft, or 3.70 cubic yards.
- Should I order extra?
- Usually, and the amount depends on the subgrade and the pour. The overage field adds whatever percentage you decide to the order quantity and shows the result separately, so the geometric volume stays visible.
- Does it work in metres?
- Yes. Every dimension accepts metric units and the result is also given in cubic metres. The conversions are exact.
Behind the numbers
The methods and definitions this calculator applies, explained in full and with their sources.
Where people go next
Ordered by what usually comes next in the same job, not by keyword.