Slab or pad
Length × width × thickness
Patios, floors, paths, and flat pads.
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Concrete calculator
Use this concrete calculator to find how much concrete you need for a slab, footing, wall, or round pour. Estimate volume in cubic yards or cubic metres, calculate bag quantities, and review the formula and allowance before ordering.
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ConcreteYardQUANTITY ESTIMATE
Slab / pad estimate
Measurement system: Imperial. Planning estimate based on the dimensions and allowance shown below.
Concrete quantity estimate
Build your estimate
Choose a shape, enter measured dimensions, then review every step.
ft
ft
in
count
Choose for site conditions
%
Estimated volume with 10% extra1.36 yd³1.04 m³ · 62 80 lb bags
Details ↓Dimension guideDiagram, not to scale
Enter the dimensions of the concrete itself. This estimate does not subtract posts or wall openings.
Bag yields and product settings
Match the bag label
Yield differs by product. These common examples are editable.
Bag counts are rounded up. The 40, 50, 60, and 80 lb rows show common US products; use the package yield for your product.
Optional: price your materials
Enter local prices. No regional or supplier price is assumed.
USD
USD
Material estimate only. Delivery, taxes, labor, and supplier minimums are not included.
Choose your pour
Concrete volume calculator for slabs, footings, walls, and round holes
Pick the geometry above. The diagram, formula, and result update with it.
Strip footing
Length × width × depth
Continuous footings and straight trenches.
Open calculatorWall
Length × height × thickness
Poured walls; subtract openings separately later.
Round hole
π × radius² × depth
Post holes, piers, and round forms.
Open calculatorHow the estimate works
How to calculate concrete volume in cubic yards and cubic metres
Each dimension is converted to a common internal unit before calculating. The allowance is applied after the net geometric volume. Bag quantities use mixed concrete yield per bag and are rounded up individually.
Read the calculation guideWorked example10 × 10 × 4 in
Net volume33.33 ft³ / 1.23 yd³
At 10% allowance36.67 ft³ / 1.36 yd³
80 lb bags at 0.60 ft³ yield62 bags
The displayed total uses unrounded values. Bag yields vary by product; check the package.
Helpful details
Concrete calculator questions
Quantity estimates are only as useful as the dimensions and product information supplied.
How much concrete do I need for a pad with several sections?
Split the footprint into non-overlapping rectangles, calculate each section using its own specified thickness, and add the net volumes. Apply your chosen allowance once to the combined quantity. Shared corners should only be counted once. Supplier order increments are a separate step.
How much is a yard of concrete?
A cubic yard is 27 cubic feet, or 0.764554857984 cubic metres. Its price depends on a current local quote for the specified mix and the supplier’s charges. Multiply the charged quantity by the quoted unit price, then add applicable delivery or other quoted fees. The cost calculator uses prices you enter.
How do I calculate concrete for a slab?
Multiply the slab length by its width and thickness after converting all three dimensions to the same unit. Divide cubic feet by 27 for cubic yards, or multiply cubic feet by 0.028316846592 for cubic metres.
How many bags of concrete will I need?
Divide the volume including your chosen allowance by the mixed concrete volume listed on the product packaging. Round up to a whole bag. The bag sizes shown here use common US mixed-volume yields; check the product label or enter a custom yield for the mix available where you live.
What extra allowance should I use?
There is no single allowance that suits every site. Ground variation, formwork, access, excavation accuracy, and placement losses all affect the amount. Choose an allowance based on measured conditions and advice from your local supplier or contractor.
Does this tell me how thick a slab or footing should be?
No. This estimates material quantity from dimensions you provide. It does not size a foundation, select reinforcement, or check structural or building-code requirements. Use project plans and qualified local advice for design decisions.
From the ConcreteYard blog
Clear answers to common concrete questions
How Much Concrete Do I Need? Slab, Footing and Bag Examples
Calculate how much concrete you need from measured dimensions. Follow slab, footing and round-form examples, separate allowances, and convert volume to whole bags.
Read article ↗Concrete Price Per Yard: Calculate Cost from a Supplier Quote
Work out concrete cost per cubic yard from your supplier quote. Separate material, billed quantity, delivery and other fees, and compare ready-mix with bagged concrete.
Read article ↗Concrete Pad Calculator Examples: Cubic Yards and Bags
Estimate concrete for a rectangular pad from length, width and specified thickness. Compare cubic yards and bag counts for a 12 × 16 ft example, including a separate allowance.
Read article ↗How Many Bags of Concrete Are in a Yard?
A cubic yard is 27 cubic feet. See bag counts by package size using QUIKRETE's listed yields, plus the formula to check your own product.
Read article ↗What Does a Concrete Mix Ratio Mean?
Learn what ratios such as 1:2:3 describe, why they do not guarantee a concrete strength, and what to check before using a mix on a real project.
Read article ↗How Much Does a Yard of Concrete Weigh?
See the approximate weight of a cubic yard of normalweight concrete, the density-based calculation, and why actual concrete weights vary by mix.
Read article ↗Quantity planning only. This tool does not determine safe slab or footing dimensions, reinforcement, concrete strength, or local code compliance. Confirm site measurements and product yields before ordering.
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