Concrete Calculator
Calculate concrete volume, cubic yards, bags needed, and estimated project costs for slabs, footings, foundations, patios, driveways, and more.
Example Projects
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Results Summary
View Calculation Breakdown
Detailed Volumes Live
| Net Volume (no waste): | 33.33 ft³ |
| Waste Margin added: | +3.33 ft³ (10%) |
| Total Volume (with waste): | 36.67 ft³ |
| Cubic Yards: | 1.36 yd³ |
| Cubic Meters: | 1.04 m³ |
How this was calculated:
Everything behind the Concrete Calculator
Formulas, reference charts, and detailed answers — expand any section you need.
How Many Bags of Concrete Do You Need?
For smaller projects like post settings, small garden slabs, or stairs, using bagged pre-mixed concrete is common. The quantity of bags depends entirely on the size/weight of bags you purchase:
Concrete Bag Yield Chart
| Bag Weight (lbs) | Cubic Feet Yield Per Bag | Bags Needed per Cubic Yard (27 ft³) |
|---|---|---|
| 80 lb | 0.60 ft³ | 45 bags (90 bags per 2 cubic yards) |
| 60 lb | 0.45 ft³ | 60 bags |
| 50 lb | 0.375 ft³ | 72 bags |
| 40 lb | 0.30 ft³ | 90 bags |
Example calculation: If your slab requires 30 cubic feet of concrete and you purchase 80 lb bags:
30 ft³ ÷ 0.60 ft³/bag = 50 bags required.
How to Use the Concrete Calculator
Estimating concrete volume accurately is essential to avoid order shortages or buying expensive excess materials. Follow these step-by-step instructions to compute your requirements:
- Select Project Type: Choose the shape that matches your structural element. We support rectangular slabs/footings, columns/cylinders, round slabs, walls, stairs, and manual volume input.
- Input Dimensions: Enter length, width, depth, or diameter. Use the dropdown menus to switch units (Inches, Feet, Yards, Centimeters, or Meters). The calculator will normalize units automatically.
- Set Waste Factor: Slabs can bow, and subgrade dirt levels settle unequally. Adjust the waste factor slider (10% is standard) to add extra safety margin.
- Choose Bag Size: Select the dry mix bag size you plan to purchase (40 lb, 50 lb, 60 lb, or 80 lb) to calculate the exact bag count needed.
- Enter Costs (Optional): Enter the price per cubic yard or local concrete supply price to obtain a raw material cost projection.
Concrete Volume Formula Explained
The basic formula for rectangular concrete volume is:
Where variables correspond to:
- V: Volume (in cubic feet)
- L: Length of the pour area (in feet)
- W: Width of the pour area (in feet)
- D: Depth or thickness of the pour area (in feet, calculated as inches divided by 12)
For circular structures (like columns or round slabs), use the formula:
- V: Volume (in cubic feet)
- π: Pi (approximately 3.14159)
- r: Radius (half of the diameter, in feet)
- h: Height or depth (in feet)
Once the volume in cubic feet is calculated, convert it to cubic yards (which is the standard pricing and ordering unit for ready-mix trucks) by dividing the total cubic feet by 27:
Concrete Cost Estimation Guide
Concrete project costs depend on the delivery type (ready-mix truck vs. bagged concrete) and labor requirements:
- Ready-Mix Concrete: Typically ranges from $120 to $180 per cubic yard. Most companies enforce a minimum charge or delivery fee for loads under 5 cubic yards. Expect delivery surcharges, waiting-time charges, or fuel fees.
- Bagged Concrete: Priced at $4.50 to $9.00 per bag depending on the brand and mix type (e.g., standard, fast-setting, high-strength). Buying concrete in bags translates to approximately $400 to $800 per cubic yard, making it more expensive for volumes larger than 1.5 yards.
- Labor Considerations: Pouring concrete is physically demanding. Contractor labor costs typically range from $6.00 to $15.00 per square foot, which covers subgrade grading, laying forms, installing rebar reinforcement, pouring, and finishing (broom or smooth finish).
Slab Thickness Guide
Reserved for light, non-structural decorative applications, top dressings, or concrete countertops.
Standard thickness for residential walkways, patios, storage shed bases, and interior floors.
Required for residential driveways supporting light trucks/SUVs, garage floors, and hot tub platforms.
Designed for industrial parking pads, commercial truck parking, and municipal roadways.
Measurement Units Explained
Equal to 27 cubic feet. The standard unit for ordering ready-mix concrete trucks.
Equal to 12" × 12" × 12". Used primarily to calculate small batches and dry bag yields.
Used in metric systems. 1 m³ is equal to 35.31 cubic feet or 1.308 cubic yards.
Concrete Calculator for Foundations, Footings, and Walls
Here are common residential pours with typical specifications:
- Small Garden Patios: Typically 10 ft × 12 ft poured at 4 inches thick. Needs 1.48 cubic yards (or 67 bags of 80 lb concrete).
- Standard Residential Driveways: Typically 10 ft × 40 ft poured at 6 inches thick. Needs 7.41 cubic yards (or 334 bags of 80 lb concrete). Ready-mix truck is highly recommended.
- Two-Car Garage Floor: Typically 20 ft × 20 ft poured at 4 inches thick. Needs 4.94 cubic yards.
- Pier Footings: Often 2 ft × 2 ft cylindrical holes dug to 1 foot deep. Needs 0.12 cubic yards per hole.