Calculate how much concrete you need for a slab, patio, driveway, wall, footing, or column. See cubic yards, cubic feet, cubic meters, waste allowance, optional bag estimates, and cost.
Concrete Calculator
Enter your project details below and press Calculate for an instant estimate.
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This calculator estimates concrete quantity from dimensions. Footing size, reinforcement, soil bearing, frost depth, and structural requirements should come from the applicable plans, codes, or qualified professional.
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Waste Allowance
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The waste percentage is a planning allowance for uneven subgrade, spillage, and measurement variation. It is not part of the calculated geometric volume, and the calculator always shows both numbers separately.
Ready-mix suppliers may have their own minimums or order increments. This rounds only the displayed planning amount, labeled separately from your calculated quantity.
Optional: Estimate Bags & Material Cost
Use the yield printed on the specific concrete-mix bag you plan to buy. Product yields vary by brand, bag size, and mix design.
Example only. Replace with the yield and label on your product bag.
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Material-only estimate based on the values entered. It does not include delivery, short-load fees, tax, labor, reinforcement, forms, grading, or equipment unless you add them yourself.
Concrete quantity is based on volume. For a rectangular slab, patio, driveway section, footing, or wall, the basic calculation is length times width times thickness equals volume.
The most common mistake is mixing units. If the length and width are measured in feet but the thickness is entered in inches, the thickness must first be converted to feet. For example, suppose a slab is 12 feet long, 20 feet wide, and 4 inches thick. Four inches equals 4 divided by 12, which is about 0.3333 feet.
Now multiply: 12 × 20 × 0.3333 is approximately 80 cubic feet. One cubic yard contains 27 cubic feet, so 80 divided by 27 is approximately 2.96 cubic yards. That is the geometric concrete volume before adding any planning allowance.
Visual: Why Thickness Must Be Converted
Length and width are usually measured in feet, but thickness is often measured in inches. Dividing the inch measurement by 12 converts it to feet so that feet times feet times feet produces cubic feet.
Converting slab thickness from inches to feet
Step
Calculation
Convert thickness
4 inches ÷ 12 = 0.3333 feet
Multiply consistent units
feet × feet × feet = cubic feet
Visual: Slab Volume
A slab's volume is its length times its width times its thickness. All three dimensions must be in the same unit before multiplying.
Dimensions used to calculate slab volume
Dimension
Role in Formula
Length
First multiplied dimension
Width
Second multiplied dimension
Thickness
Third multiplied dimension, converted to feet if measured in inches
Why Is Concrete Measured in Cubic Yards?
Concrete is a three-dimensional material. Square footage measures area. Concrete quantity requires volume, which means a slab's thickness matters just as much as its length and width. A 20 by 20 foot slab that is four inches thick does not require the same volume as a 20 by 20 slab that is six inches thick.
In U.S. ready-mix construction, concrete volume is commonly discussed in cubic yards. A cubic yard is 3 feet by 3 feet by 3 feet, which equals 27 cubic feet.
Visual: 27 Cubic Feet Equals 1 Cubic Yard
A cubic yard is arranged as 3 layers of 3 by 3 one-foot cubes, for 27 one-foot cubes in total.
How 27 cubic feet make one cubic yard
Arrangement
Total Cubic Feet
3 × 3 × 3 one-foot cubes
27 cubic feet = 1 cubic yard
How Do I Convert Cubic Feet to Cubic Yards?
Divide by 27.
Cubic yards = cubic feet ÷ 27
Example: 135 cubic feet divided by 27 equals 5 cubic yards. To move the other direction, cubic feet equals cubic yards times 27, so 5 cubic yards equals 135 cubic feet.
How Much Concrete for a 4-Inch Slab?
Start by converting four inches to feet: 4 divided by 12 equals 1/3 foot. Then multiply length times width times 1/3.
Example: 10 ft × 10 ft slab
10 × 10 × 1/3 = 33.33 cubic feet. Divide by 27: 33.33 ÷ 27 is approximately 1.23 cubic yards, before any waste or field allowance.
Example: 12 ft × 12 ft slab
12 × 12 × 1/3 = 48 cubic feet. 48 ÷ 27 is approximately 1.78 cubic yards.
The calculator above uses the exact dimensions you enter instead of relying on generic square-foot rules.
Why Add Extra Concrete?
The mathematically calculated shape assumes a perfect project. Real pours may involve uneven subgrade, excavation variation, forms that are not perfectly exact, spillage, material remaining in equipment, and measurement error.
ACI educational material discusses adding an allowance beyond the calculated volume to account for conditions such as uneven subgrade, settlement, spillage, and waste. That does not mean every job needs the same percentage. CalculateThisWay therefore lets you choose 0%, 5%, 10%, 15%, or a custom allowance.
Visual: Raw Volume vs. Waste Allowance
The calculator always separates the raw geometric volume from the waste allowance, so you can see exactly what came from your measurements and what came from your chosen allowance.
Example split between raw volume and a 10 percent waste allowance
Component
Amount
Calculated geometric volume
2.96 cubic yards
10% waste allowance
0.30 cubic yards
Planning quantity
3.26 cubic yards
The page above always shows the raw geometric volume separately so you know what part came from measurements and what part came from the chosen allowance.
Is 10% Extra Concrete Always Required?
No. Ten percent is a common planning choice, not a universal engineering requirement. The appropriate allowance can depend on project size, subgrade condition, form accuracy, supplier practices, placement method, and site conditions.
ACI educational guidance notes that smaller quantities may sometimes use larger percentage allowances than larger placements. You should select the allowance appropriate to your project rather than having a calculator secretly add one for you.
How Much Concrete for a Patio?
A patio is usually calculated like a rectangular slab. Measure length, width, and thickness. For example, 15 ft by 12 ft by 4 in. Four inches is 0.3333 ft. Volume: 15 × 12 × 0.3333 is approximately 60 cubic feet. Cubic yards: 60 ÷ 27 is approximately 2.22 cubic yards. With a 10% planning allowance: 2.22 × 1.10 is approximately 2.44 cubic yards.
How Much Concrete for a Driveway?
Use the same volume formula. However, the correct driveway thickness is not something a calculator should invent. Thickness can depend on vehicle loads, subgrade, reinforcement, local requirements, and project specifications. Enter the thickness specified for your actual project, and the calculator determines volume. It should estimate material quantity, not perform structural pavement design.
How Much Concrete for a Wall?
A solid rectangular concrete wall uses length times height times thickness. Suppose 20 ft long, 8 ft high, 6 inches thick. Six inches is 0.5 ft. Volume: 20 × 8 × 0.5 = 80 cubic feet. 80 ÷ 27 is approximately 2.96 cubic yards. Then apply the selected planning allowance.
Openings such as doors or windows should be subtracted only if they genuinely displace concrete in the wall design. If subtraction features are added, they should be displayed separately so the math stays transparent.
How Much Concrete for a Footing?
A rectangular footing also uses length times width times depth. If several identical footings are required, multiply by the quantity. For example, 8 ft long, 2 ft wide, 1 ft deep, four identical footings. One footing: 8 × 2 × 1 = 16 cubic feet. Four: 64 cubic feet. 64 ÷ 27 is approximately 2.37 cubic yards.
The calculator does not determine whether those footing dimensions are structurally adequate. ACI residential concrete guidance makes clear that footings are part of a larger structural system subject to applicable codes and project requirements.
How Do I Calculate Concrete for a Round Column?
A round column is a cylinder.
Volume = π × radius² × height
If the column diameter is 2 feet, the radius is 1 foot. If it is 8 feet tall, volume is π × 1² × 8, approximately 25.13 cubic feet. Convert: 25.13 ÷ 27 is approximately 0.93 cubic yards. Then multiply by the number of identical columns.
Visual: Rectangular vs. Round Pour
A rectangular pour uses length times width times depth. A round pour, such as a column, uses pi times radius squared times height.
Formula comparison between rectangular and round pours
Shape
Formula
Rectangular (slab, wall, footing)
Length × Width × Depth
Round (column)
π × radius² × height
How Many Bags of Concrete Do I Need?
Bag count depends on the actual yield of the product. The important number is not merely whether the bag weighs 40 lb, 60 lb, or 80 lb. Different products and mixes can have different stated yields. Use the yield printed on the product packaging.
Always round the bag count upward, because a fraction of a bag is still another bag. CalculateThisWay lets you enter the product's stated yield instead of assuming one generic yield applies to every brand and mix.
Ready-Mix Concrete vs Bagged Concrete
Small repairs or pours may be practical with bagged concrete. Larger placements are often supplied as ready-mixed concrete by volume. The calculator above does not decide which purchase method is appropriate for a specific project. It simply provides volume, an optional bag estimate, and an optional material cost. You can then compare supplier requirements and product instructions.
How Much Does Concrete Cost?
If a supplier quotes a price per cubic yard, multiply planning cubic yards by the price per cubic yard. Example: 3.5 cubic yards at $175 per cubic yard is an estimated concrete material cost of 3.5 × $175 = $612.50.
That is not necessarily the final project or delivery cost. There may also be delivery charges, short-load fees, tax, labor, forms, reinforcement, equipment, and site preparation. The calculator above labels this result estimated concrete material cost.
Concrete Calculator vs Square Footage Calculator
Square footage measures two-dimensional area. Concrete requires three-dimensional volume. If you only know the floor or slab area, the Square Footage Calculator can help determine the area. Once you know length, width, and concrete thickness, the Concrete Calculator above determines volume.
Metric Concrete Calculation
Metric volume is particularly straightforward when all measurements are in meters. Example: 6 m long, 4 m wide, 0.10 m thick. Volume: 6 × 4 × 0.10 = 2.4 cubic meters. If thickness is entered as centimeters, convert it: 10 cm = 0.10 m. The same principle applies in either measurement system: all dimensions must be expressed in compatible units before multiplying.
Why Your Supplier's Quantity May Differ
A calculator uses the dimensions and assumptions you enter. A supplier, contractor, or engineer may account for field measurements, delivery increments, minimum orders, pump requirements, uneven excavation, construction tolerances, and job-specific waste. The calculated result is therefore a planning estimate. It should not replace the construction documents or a professional quantity takeoff for a critical project.
The Bottom Line
Concrete quantity is a volume problem. For a rectangular pour: length times width times thickness. For a round column: pi times radius squared times height. Then convert the volume to the unit used by your supplier. In U.S. work, 27 cubic feet equals 1 cubic yard. CalculateThisWay shows the raw volume first, your waste allowance separately, and the final planning quantity clearly, so you understand every part of the answer.
Worked Concrete Examples
The examples below use the exact same calculation engine as the calculator above. Values are computed live in JavaScript rather than typed in as fixed text, so they will always match what the calculator itself would return for these inputs.
Slab: 12 ft × 20 ft, 4 in
Slab: 10 ft × 10 ft, 4 in
Wall: 20 ft × 8 ft, 6 in thick
4 Footings: 8 ft × 2 ft × 1 ft each
Round Column: 2 ft diameter, 8 ft high
Metric Slab: 6 m × 4 m, 0.10 m
Try It Yourself
Slab / Patio / Driveway. Length 12 ft. Width 20 ft. Thickness 4 in. Waste allowance 10%.
What is the planning quantity in cubic yards?
80 cubic feet geometric volume, which is about 2.96 cubic yards. With a 10% waste allowance, the planning quantity is about 3.26 cubic yards.
Which Pour Type Should I Select?
Questions People Ask
How much concrete do I need?
Enter your project dimensions, or a diameter and height for a round column, into the calculator above. It multiplies length by width by thickness, or uses the cylinder formula for a column, converts the result to cubic yards, cubic feet, and cubic meters, and adds your chosen waste allowance.
How do I calculate concrete?
For a rectangular pour, multiply length by width by thickness after converting thickness to the same unit as length and width. For a round column, multiply pi by the radius squared by the height.
How many cubic feet are in a cubic yard?
One cubic yard equals 27 cubic feet, since a cubic yard measures 3 feet by 3 feet by 3 feet.
How do I calculate cubic yards?
Calculate the volume in cubic feet, then divide by 27. For example, 80 cubic feet divided by 27 is about 2.96 cubic yards.
How much concrete do I need for a 4-inch slab?
Convert 4 inches to feet, which is 4 divided by 12, or about 0.3333 feet, then multiply by the slab's length and width in feet. A 10 ft by 10 ft slab at 4 inches needs about 1.23 cubic yards before waste.
How much concrete for a 10x10 slab?
A 10 ft by 10 ft slab at 4 inches thick is about 33.33 cubic feet, or roughly 1.23 cubic yards, before any waste allowance.
How much concrete for a 12x12 slab?
A 12 ft by 12 ft slab at 4 inches thick is 48 cubic feet, or about 1.78 cubic yards, before any waste allowance.
How much concrete for a 20x20 slab?
Volume depends on thickness. At 4 inches, a 20 ft by 20 ft slab is about 133.33 cubic feet, or roughly 4.94 cubic yards, before waste. Enter your exact thickness in the calculator above for a precise figure.
How much concrete for a patio?
Measure the patio's length, width, and thickness, then use the Slab, Patio, Driveway mode above. A 15 ft by 12 ft patio at 4 inches thick is about 2.22 cubic yards before waste.
How much concrete for a driveway?
Use the same length times width times thickness formula as a slab. Driveway thickness depends on vehicle loads, subgrade, and local requirements, so enter the thickness specified for your project instead of a generic guess.
How much concrete for a wall?
Multiply wall length by height by thickness. A 20 ft long, 8 ft high wall at 6 inches thick is 80 cubic feet, or about 2.96 cubic yards, before waste.
How much concrete for a footing?
Multiply footing length by width by depth, then multiply by the number of identical footings. Four footings each 8 ft by 2 ft by 1 ft total 64 cubic feet, or about 2.37 cubic yards, before waste.
How do I calculate a round concrete column?
Divide the diameter by 2 to get the radius, then use pi times radius squared times height. A 2 ft diameter, 8 ft tall column is about 25.13 cubic feet, or roughly 0.93 cubic yards.
How much extra concrete should I add?
That depends on the project. The calculator lets you choose 0 percent, 5 percent, 10 percent, 15 percent, or a custom waste allowance to plan for uneven subgrade, spillage, and measurement variation.
Should I add 10% for waste?
Ten percent is a common planning choice for many pours, but it is not mandatory. Smaller jobs sometimes use a larger percentage allowance, and larger placements sometimes use a smaller one.
Is 10% waste always required?
No. Waste allowance is a planning choice based on project size, subgrade condition, form accuracy, and supplier practices, not a fixed engineering requirement.
How do I convert inches of thickness to feet?
Divide the thickness in inches by 12. For example, 4 inches divided by 12 equals about 0.3333 feet.
How many bags of concrete do I need?
Divide the volume you need by the yield printed on your specific concrete mix bag, then round up, since a fraction of a bag still requires a full bag.
Are all bagged-concrete yields the same?
No. Yield varies by product, bag size, and mix design. Always use the yield listed on the bag you plan to buy instead of a generic assumption.
How do I calculate concrete bag count?
Enter the yield per bag from the product packaging into the optional bag section, and the calculator divides your planning volume by that yield and rounds up to a whole number of bags.
How much does concrete cost per yard?
Ready-mix pricing varies by region, supplier, and order size. Enter your supplier's quoted price per cubic yard, or cubic meter, into the optional cost field for a material-only estimate.
Does this include delivery fees?
No. The cost estimate covers material only, based on the price you enter. It does not include delivery charges, short-load fees, tax, labor, forms, reinforcement, or equipment unless you add them yourself.
Should I round cubic yards up?
You can optionally round the planning amount up to the nearest 0.1, 0.25, 0.5, or 1 unit. This is a convenience for ordering, not a required step, since suppliers may have their own minimums or increments.
Can I use this calculator for structural design?
No. This calculator estimates concrete volume from the dimensions you enter. It does not replace structural design, reinforcement planning, or a review of applicable codes by a qualified professional.
Can I calculate concrete in cubic meters?
Yes. Switch the unit system to Metric to enter dimensions in meters and centimeters and see your result in cubic meters, with cubic yards shown for reference.
How many cubic yards are in a cubic meter?
One cubic meter is about 1.30795 cubic yards, based on the NIST conversion of approximately 0.7645549 cubic meters per cubic yard.
Is square footage the same as concrete volume?
No. Square footage measures two-dimensional area. Concrete volume also depends on thickness, so the same square footage can require very different amounts of concrete depending on how thick the pour is.
What is the difference between a Concrete Calculator and Square Footage Calculator?
The Square Footage Calculator finds the area of a space. The Concrete Calculator takes that length and width plus a thickness to find the three-dimensional volume of concrete needed.
Geometric volume is calculated from the exact dimensions entered, converting all length units to a single consistent unit before multiplying.
The selected waste allowance is always shown separately from the calculated geometric volume, and is never silently added without being displayed.
Cubic yard conversions use 27 cubic feet per cubic yard, and cubic meter conversions use the NIST figure of approximately 0.7645549 cubic meters per cubic yard.
Bag estimates depend entirely on the yield you enter and do not assume a universal yield for any bag weight or brand.
Cost estimates are material-only, based on the price you enter, and do not include delivery, tax, labor, forms, reinforcement, grading, or equipment.
This calculator does not perform structural design, reinforcement planning, or code compliance review for footings, walls, or slabs.
This calculator estimates concrete volume from the dimensions you enter. It does not perform structural design, account for reinforcement, subgrade preparation, frost depth, local building codes, or supplier minimums. For structural requirements, consult the applicable plans, codes, or a qualified professional.