Concrete Calculator
Calculate the exact amount of concrete needed for slabs, footings, columns, and stairs. Get results in cubic yards, cubic meters, and bags required.
Project Type
Dimensions
Number of identical slabs/footings
Additional Options
Typically 5-10% for waste and spillage
Concrete Needed
3.7 cubic yards
3.1 cubic meters
How to Calculate Concrete Volume
Calculating concrete accurately is essential for any construction project. Too little concrete means delays and additional delivery fees, while too much wastes money. This free concrete calculator helps you determine exactly how much concrete you need for slabs, footings, columns, and stairs.
Concrete Volume Formula
For rectangular slabs and footings, use this formula:
- Volume (cubic feet) = Length (ft) × Width (ft) × Thickness (ft)
- Cubic Yards = Cubic Feet ÷ 27
For circular columns and piers:
- Volume (cubic feet) = π × (Radius)² × Height
- Radius = Diameter ÷ 2
Standard Concrete Slab Thickness
- 3-4 inches: Walkways, patios, residential floors
- 5-6 inches: Driveways, garage slabs, light vehicle traffic
- 6-8 inches: Heavy vehicle traffic, commercial applications
- 8+ inches: Industrial floors, heavy equipment areas
Concrete Bag Coverage
Pre-mixed concrete bags come in different sizes. Here's what each covers:
- 40 lb bag: 0.30 cubic feet (0.011 cubic yards)
- 60 lb bag: 0.45 cubic feet (0.017 cubic yards)
- 80 lb bag: 0.60 cubic feet (0.022 cubic yards)
For large projects over 1 cubic yard, ready-mix delivery is more cost-effective than bagged concrete.
Ready-Mix vs. Bagged Concrete
Use Ready-Mix When:
- Project requires more than 1 cubic yard
- You need continuous pour for structural integrity
- Time is limited
- Professional finish is required
Use Bagged Concrete When:
- Small repairs or projects under 0.5 cubic yards
- Access is difficult for concrete trucks
- Working in stages
- Setting posts or small pads
Waste Factor Recommendations
Always add extra concrete for waste, spillage, and subgrade irregularities:
- 5%: Perfectly prepared site, experienced crew
- 10%: Standard recommendation for most projects
- 15-20%: Uneven subgrade or complex shapes
Important Notes
This calculator provides estimates for planning purposes. Actual concrete needs may vary based on site conditions, formwork accuracy, and subgrade preparation. Always consult with your concrete supplier for final quantities.
Concrete prices vary by region, delivery distance, and concrete strength (PSI rating). The cost estimate uses an average of $125 per cubic yard for ready-mix concrete in Canada.
For structural applications, always consult a licensed engineer to ensure proper concrete strength, reinforcement, and thickness specifications.
Frequently Asked Questions
How much concrete do I need for a slab?
To calculate concrete for a slab, multiply length × width × thickness (all in feet), then divide by 27 to get cubic yards. Add 5-10% extra for waste. For example, a 10×10 ft slab that's 4 inches thick needs: 10 × 10 × 0.33 = 33 cubic feet ÷ 27 = 1.2 cubic yards.
How many bags of concrete do I need?
A standard 80 lb bag covers 0.6 cubic feet or 0.022 cubic yards. Divide your total cubic yards by 0.022 to find the number of 80 lb bags needed. For smaller projects, bagged concrete works well. For anything over 1 cubic yard, order ready-mix delivery.
How thick should a concrete slab be?
Standard residential slabs are 4 inches thick for patios and walkways. Driveways and garage slabs should be 6 inches thick to support vehicle weight. Heavy-duty commercial applications may need 8+ inches. Always check local building codes.
What is the cost of concrete per cubic yard?
Ready-mix concrete typically costs $100-$150 per cubic yard in Canada, depending on location, concrete strength (PSI), special additives, and delivery distance. Short loads (less than minimum delivery) may incur additional fees.
Should I order extra concrete?
Yes, always order 5-10% extra concrete to account for spillage, uneven subgrade, and minor calculation errors. Running short during a pour is more expensive than ordering extra, as you'll pay rush delivery fees and risk cold joints in your slab.