Concrete Calculator: Calculate Cubic Yards for Any Project
A concrete calculator is an essential construction tool that accurately computes the volume of concrete needed for slabs, footings, walls, columns, circular structures, curbs, gutters, and stairs measured in cubic yards. By inputting project dimensions and specifications, this calculator determines precise material quantities, converts to bags or ready-mix truck loads, and provides cost estimates—helping contractors, builders, and DIY enthusiasts order the exact amount of concrete for foundations, driveways, patios, sidewalks, and structural elements while avoiding costly shortages or expensive over-ordering waste in residential and commercial construction projects.
🏗️ Interactive Concrete Calculator
Select project type and calculate concrete needed
Slab, Square Footing, or Wall Calculator
For rectangular shapes: driveways, patios, foundations, walls
Column, Round Footing, or Cylindrical Hole Calculator
For circular columns, pier footings, or cylindrical excavations
Circular Slab or Tube Calculator
For round patios, slabs, or concrete tubes/pipes
Curb and Gutter Barrier Calculator
For street curbs, parking lot barriers, or drainage gutters
Stairs/Steps Calculator
For concrete stairs, landings, and steps
Understanding Concrete Volume Calculations
Concrete volume is measured in cubic yards in the United States. One cubic yard equals 27 cubic feet (3 feet × 3 feet × 3 feet).
Basic Volume Formula
Concrete Volume Formula:
\[ V_{\text{cubic yards}} = \frac{L \times W \times T}{27} \]
Where:
\[ L = \text{Length (feet)}, \quad W = \text{Width (feet)}, \quad T = \text{Thickness (feet)} \]
Note: Convert inches to feet by dividing by 12
Formulas by Project Type
1. Rectangular Slab, Wall, or Square Footing
Rectangular Volume:
\[ V = \frac{L \times W \times T}{27} \]
If thickness in inches:
\[ V = \frac{L \times W \times (T/12)}{27} = \frac{L \times W \times T}{324} \]
Example: Driveway Slab
Dimensions: 20' long × 10' wide × 4" thick
Step 1: Convert thickness to feet: 4" ÷ 12 = 0.333 feet
Step 2: Calculate volume:
\[ V = \frac{20 \times 10 \times 0.333}{27} = \frac{66.6}{27} = 2.47 \text{ cubic yards} \]
Order: 2.5 cubic yards (round up)
2. Cylindrical Column or Round Footing
Cylinder Volume:
\[ V = \frac{\pi r^2 h}{27} \]
Where:
\[ r = \text{Radius in feet} = \frac{\text{Diameter in inches}}{24} \]
\[ h = \text{Height in feet} \]
Or using diameter:
\[ V = \frac{\pi d^2 h}{108} \quad \text{(d in feet)} \]
Example: Concrete Column
Dimensions: 12" diameter × 4' height
Step 1: Convert diameter to feet: 12" ÷ 12 = 1 foot
Step 2: Calculate radius: r = 0.5 feet
Step 3: Calculate volume:
\[ V = \frac{3.14159 \times 0.5^2 \times 4}{27} = \frac{3.14159}{27} = 0.116 \text{ cubic yards} \]
For 10 columns: 0.116 × 10 = 1.16 cubic yards
3. Circular Slab
Circular Slab Volume:
\[ V = \frac{\pi r^2 t}{27} \]
Where:
\[ r = \text{Radius (feet)}, \quad t = \text{Thickness (feet)} \]
4. Curb and Gutter
Curb Volume:
\[ V = \frac{L \times W \times H}{27} \]
Where:
\[ L = \text{Length (feet)}, \quad W = \text{Width (feet)}, \quad H = \text{Height (feet)} \]
5. Stairs
Stair Volume Approximation:
\[ V = \frac{W \times D \times H \times N}{54} \]
Where:
\[ W = \text{Width (feet)}, \quad D = \text{Tread depth (feet)} \]
\[ H = \text{Riser height (feet)}, \quad N = \text{Number of steps} \]
Factor of 54 = 27 × 2 (average step volume)
Complete Calculation Examples
Example 1: Patio Slab
Project: 12' × 10' patio, 4" thick
Calculation:
\[ V = \frac{12 \times 10 \times (4/12)}{27} = \frac{12 \times 10 \times 0.333}{27} = \frac{40}{27} = 1.48 \text{ yd}^3 \]
Order: 1.5 cubic yards
80-lb bags: 1.48 × 45 = 67 bags
Cost estimate: Ready-mix $120/yd³ × 1.5 = $180
Example 2: Foundation Footings
Project: 8 round footings, 18" diameter × 3' deep
Per footing:
\[ V = \frac{\pi \times (0.75)^2 \times 3}{27} = \frac{3.14159 \times 0.5625 \times 3}{27} = 0.196 \text{ yd}^3 \]
Total: 0.196 × 8 = 1.57 cubic yards
Order: 2 cubic yards (includes waste)
Example 3: Concrete Stairs
Project: 4' wide stairs, 5 steps, 11" tread, 7" riser
Calculation:
Convert to feet: Tread = 0.917 ft, Riser = 0.583 ft
\[ V = \frac{4 \times 0.917 \times 0.583 \times 5}{54} = \frac{10.71}{54} = 0.198 \text{ yd}^3 \]
Order: 0.25 cubic yards or 12 bags (80-lb)
Concrete Coverage Reference
| Thickness | Square Feet per Cubic Yard | Cubic Yards per 100 Sq Ft |
|---|---|---|
| 4 inches | 81 sq ft | 1.23 yd³ |
| 5 inches | 65 sq ft | 1.54 yd³ |
| 6 inches | 54 sq ft | 1.85 yd³ |
| 8 inches | 41 sq ft | 2.47 yd³ |
| 10 inches | 32 sq ft | 3.09 yd³ |
| 12 inches | 27 sq ft | 3.70 yd³ |
Concrete Bag Calculations
Bags per Cubic Yard
| Bag Size | Yield per Bag | Bags per Cubic Yard |
|---|---|---|
| 40-pound bag | 0.011 yd³ | 90 bags |
| 60-pound bag | 0.017 yd³ | 60 bags |
| 80-pound bag | 0.022 yd³ | 45 bags |
Standard Concrete Thicknesses
Recommended Thickness by Application
- Sidewalks: 4 inches minimum
- Patios: 4 inches (residential), 5-6 inches (heavy use)
- Driveways: 4 inches (cars only), 5-6 inches (trucks/RVs)
- Garage floors: 4-6 inches with wire mesh reinforcement
- Basement floors: 4 inches minimum with vapor barrier
- Foundation footings: Width = 2× wall thickness, depth = frost line
- Slab-on-grade: 4-6 inches with gravel base
Adding Waste Factor
⚠️ Always Add Extra Concrete
Recommended waste allowance:
- Simple projects: Add 5-10% extra
- Complex shapes: Add 10-15% extra
- Deep footings/columns: Add 10-15% extra
- Stairs/irregular: Add 15-20% extra
Why add extra:
- Measurement errors and irregular excavations
- Concrete spillage during placement
- Uneven subgrade requiring more material
- Better to have extra than run short mid-pour
Ready-Mix vs. Bagged Concrete
When to Use Ready-Mix Trucks
- Projects over 1 cubic yard: More economical than bags
- Large slabs: Driveways, patios, foundations
- Time savings: No mixing required
- Consistent quality: Professional batching
- Cost: $100-$150 per cubic yard delivered
When to Use Bagged Concrete
- Small projects: Under 0.5 cubic yards
- Repairs: Patches, post holes, small footings
- Remote locations: No truck access
- DIY projects: Mix as needed, work at own pace
- Cost: $4-$8 per 80-lb bag
Concrete Mixing Ratios
Standard Mix Proportions
Basic Concrete Mix (by volume):
\[ 1 \text{ part cement} : 2 \text{ parts sand} : 3 \text{ parts gravel} \]
Water-cement ratio: 0.5 (1 gallon water per 2 gallons cement)
Mix Strength Classifications
| Mix Type | Strength (PSI) | Common Uses |
|---|---|---|
| Standard Mix | 2,500-3,000 | Sidewalks, patios, slabs |
| High-Strength | 4,000-5,000 | Driveways, foundations, commercial |
| Maximum | 6,000+ | Structural, heavy-duty industrial |
Installation Tips
Professional Concrete Pouring Guidelines:
- Prepare subgrade: Compact soil, add 4-6" gravel base
- Install forms: Level, braced, properly staked
- Add reinforcement: Wire mesh or rebar as required
- Check weather: Pour between 50-85°F, avoid freezing or extreme heat
- Pour continuously: Don't stop mid-section to avoid cold joints
- Screed level: Use straight edge immediately after pouring
- Float surface: Bull float for smooth finish
- Add control joints: Every 8-10 feet to control cracking
- Cure properly: Keep moist for 7 days minimum
- Protect surface: Cover from rain, direct sun during curing
Common Mistakes to Avoid
❌ Concrete Calculation Errors
- Not converting units: Mixing feet and inches in formulas
- Forgetting thickness conversion: Inches must be divided by 12
- No waste factor: Running short ruins project timing
- Wrong cubic yard conversion: Using 28 instead of 27
- Inadequate subgrade prep: Leads to settling and cracking
- No reinforcement: Concrete is strong in compression, weak in tension
- Poor curing: Reduces final strength by 50% or more
- Adding too much water: Weakens concrete significantly
Cost Estimation
Material Costs
- Ready-mix concrete: $100-$150 per cubic yard delivered
- Short load fee: $50-$100 for loads under minimum (usually 3-4 yards)
- 80-lb bagged concrete: $4-$8 per bag
- Wire mesh (6×6): $0.30-$0.50 per square foot
- Rebar: $0.50-$1.50 per linear foot
- Gravel base: $30-$50 per cubic yard
Labor Costs
- Professional installation: $4-$8 per square foot
- Site preparation: $2-$4 per square foot
- Decorative finishes: Additional $2-$10 per square foot
- Stamped concrete: $8-$18 per square foot
Frequently Asked Questions
How many cubic yards of concrete do I need?
Calculate volume: Length × Width × Thickness (all in feet) ÷ 27 = cubic yards. Example: 10' × 10' × 4" thick: 10 × 10 × 0.333 ÷ 27 = 1.23 cubic yards. Round up and add 5-10% waste. For complex shapes, use specialized formulas for cylinders (πr²h) or irregular shapes. Always order slightly more than calculated.
How many 80-pound bags equal one cubic yard?
One cubic yard requires approximately 45 bags of 80-pound concrete mix. Each 80-lb bag yields 0.022 cubic yards (0.6 cubic feet). For smaller projects: 60-lb bags need 60 per yard, 40-lb bags need 90 per yard. Bagged concrete is economical for projects under 0.5 cubic yards; use ready-mix for larger projects.
What thickness should concrete be?
Standard thicknesses: sidewalks 4 inches, patios 4-5 inches, driveways 4-6 inches (6" for trucks), garage floors 4-6 inches with reinforcement, basement slabs 4 inches minimum. Increase thickness for heavy loads, poor soil conditions, or no reinforcement. Footings require width = 2× wall thickness and depth below frost line.
How do I calculate concrete for round footings?
Use cylinder formula: Volume = πr²h ÷ 27 for cubic yards. Convert diameter to feet, calculate radius (diameter ÷ 2), multiply by height in feet. Example: 12" diameter × 3' deep: r = 0.5', volume = 3.14159 × 0.5² × 3 ÷ 27 = 0.087 cubic yards per footing. Multiply by number of footings needed.
Should I order ready-mix or use bagged concrete?
Use ready-mix for projects over 1 cubic yard—more economical, faster, consistent quality. Costs $100-$150/yard delivered. Use bagged concrete for small repairs, post holes, or projects under 0.5 yards. Bags cost $4-$8 each (80-lb). Break-even point is approximately 1 cubic yard (45 bags). Consider convenience, time, and access.
How much does concrete cost per cubic yard?
Ready-mix concrete costs $100-$150 per cubic yard delivered, varying by region, mix strength, and additives. Minimum delivery usually 3-4 yards; short loads incur $50-$100 surcharge. Total installed cost (including labor) ranges $4-$8 per square foot for standard slabs. Decorative finishes, stamps, or colored concrete add $2-$10 per square foot.
Key Takeaways
Calculating concrete volume requires understanding dimensional conversions, geometric formulas, and waste factors. Accurate calculations ensure sufficient material, proper project completion, and cost-effective construction without shortages or excessive waste.
Essential principles to remember:
- 1 cubic yard = 27 cubic feet (3' × 3' × 3')
- Basic formula: Length × Width × Thickness (feet) ÷ 27 = cubic yards
- Convert inches to feet by dividing by 12
- Cylinder volume: πr²h ÷ 27 (r and h in feet)
- Always add 5-15% waste factor depending on project complexity
- 45 bags (80-lb) = 1 cubic yard of concrete
- Standard slab thickness: 4 inches minimum for most applications
- Ready-mix is economical for projects over 1 cubic yard
- Proper curing is essential—keep moist for 7 days
- Reinforcement (wire mesh or rebar) prevents cracking
Getting Started: Use the interactive concrete calculator at the top of this page to determine exactly how much concrete you need. Choose your project type (slab, column, circular, curb, or stairs), enter dimensions, and receive instant calculations for cubic yards, bags needed, and estimated costs. Select the appropriate calculator tab for your specific project.