Surface area
Slab area = length × width
Circle area = π × (diameter ÷ 2)²
Wall area = length × height
Concrete volume and purchase planning
Concrete Calculator
Calculate concrete for slabs, patios, driveways, circular pours, walls, and other measured sections. Combine multiple areas, add only the extra percentage you choose, and use actual supplier or package information for ready-mix, bags, weight, and cost.
LENGTHWIDTHTHICKNESS
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Enter your concrete measurements
Calculations run in this browser. This tool estimates material volume; it does not choose thickness, strength, reinforcement, mix design, or construction method.
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Calculation details
Review every section, the entered dimensions, the combined base volume, extra material, and purchase rounding.
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How concrete volume is calculated
Every section is converted to one internal unit before volumes are added.
Concrete volume
Section volume = area × thickness
Base volume = sum of section volumes
Adjusted volume = base × (1 + extra % ÷ 100)
Purchase quantity
Bags = round up(adjusted volume ÷ label yield)
Ready-mix order = round up to supplier increment
1 ft = 0.3048 m1 in = 25.4 mm1 yd³ = 27 ft³1 m³ = 1,000 L
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Worked example
This example demonstrates the formula. Its dimensions, thickness, extra percentage, and supplier increment are examples—not recommendations.
Slab12 ft × 16 ft
Thickness4 in = 0.333… ft
Base volume64 ft³ = 2.37 yd³
With 10% entered2.61 yd³
If a user separately enters a 0.25 yd³ supplier increment, 2.61 yd³ rounds to a 2.75 yd³ order quantity. If a bag data sheet states a 0.60 ft³ yield, 70.4 ft³ rounds up to 118 bags. Those figures come from the example’s user-entered options, not universal purchase advice.
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Important assumptions
This is a geometric material estimate, not structural, mix-design, code, safety, or construction advice.
- Choose thickness, concrete specification, reinforcement, joints, base preparation, and construction method from appropriate plans, requirements, product information, or qualified advice.
- Confirm measurements, placement geometry, access, supplier units, minimum orders, delivery conditions, and current prices before ordering.
- The calculator applies only the extra percentage you enter. It does not infer waste, spillage, over-excavation, grade variation, pump lines, or rejected material.
- Bag yield, bag weight, ready-mix density, and price appear only when you enter actual package or supplier information.
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Ready-mix, bags, weight, and cost
Purchase outputs are separated from the geometric result so supplier-specific inputs remain visible.
Ready-mix volume can be rounded to the order increment you enter. Bag count uses the volume yield printed on the selected package or manufacturer data sheet and always rounds to whole bags after all sections and extra material are combined. Estimated weight requires either a supplier density or an entered bag weight. Cost uses only the entered material price and excludes delivery, short-load fees, pumping, labor, equipment, tax, reinforcement, forms, base materials, finishing, disposal, and other project costs.
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Frequently asked questions
Answers describe this calculator’s behavior and limitations.
How do I calculate concrete for a slab?
Multiply length by width to find area, then multiply area by thickness using consistent units. This calculator performs those conversions and reports cubic yards, cubic feet, and cubic meters.
Can I combine a patio, walkway, and circular pad?
Yes. Add each placement as a separate section. The calculator sums the section volumes before applying the extra percentage or purchase rounding.
Does the calculator choose slab thickness?
No. Thickness depends on the project, site, loads, design, requirements, and construction plan. Enter a thickness determined from an appropriate source.
How are concrete bags calculated?
The adjusted concrete volume is divided by the volume yield you enter from the selected package or manufacturer data sheet, then rounded up to a whole bag.
Why is bag weight not enough to calculate bag count?
Bag weight is a mass, while the project estimate is a volume. Products with the same nominal weight can have different stated yields, so the calculator requires volume yield.
Does the result include a waste factor?
Only if you enter an extra percentage. The calculator does not select or recommend one.
Does cost include delivery or labor?
No. Cost uses only the material price you enter and does not automatically add taxes, delivery, short-load fees, pumping, labor, equipment, or other costs.
Can I use this for footings, columns, or structural design?
This version is limited to slab, circular, wall, and known-area volume geometry. It does not design structural elements or verify dimensions, reinforcement, strength, code, or suitability.
Formula reviewed: 2026-09-01
Exact length and volume conversions follow NIST definitions. Bag quantity requires manufacturer-stated yield; no brand yield is hard-coded.