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Concrete Calculator
Accurately estimate the amount of concrete needed for your slabs, footings, and patios. Calculate volume in cubic yards/meters and determine the number of 60lb or 80lb bags required.
*Includes 5% waste factor
How to Calculate Concrete Needs
Calculating concrete is essentially a volume problem. The formula is:
However, the tricky part is unit conversion. You typically measure length and width in feet or meters, but thickness in inches or centimeters. Our calculator handles all these conversions for you automatically.
Standard Yields
- 80lb Bag: Yields approximately 0.60 cubic feet.
- 60lb Bag: Yields approximately 0.45 cubic feet.
- 1 Cubic Yard: Equals 27 cubic feet (approx. 45 bags of 80lb concrete).
🏗️ Pro Tips for Pouring
Always Order Extra
Never order the exact amount. Subgrades are rarely perfectly flat, and forms can bow out under pressure. A 5-10% safety margin prevents the nightmare of running out of concrete mid-pour.
Water Control is Critical
Adding too much water makes the concrete easier to pour but significantly weaker and prone to cracking. Follow the manufacturer's water ratio strictly for a durable slab.
— Mark T., Civil Engineer & Construction Manager
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Add this Concrete Calculator to your construction or DIY website:
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⚠️ Common Mistake: Forgetting About Rebar and Wire Mesh
Concrete alone cracks easily. For driveways, patios, and foundations, you need rebar (for structural support) or wire mesh (for crack prevention). Don't skip this—it's not optional for most projects.
Frequently Asked Questions
How many bags of concrete do I need for a 10x10 slab?
For a 10x10 foot slab at 4 inches thick, you would need approximately 1.23 cubic yards of concrete. This translates to about 56 bags of 80lb concrete or 74 bags of 60lb concrete.
What is the difference between 60lb and 80lb concrete bags?
The main difference is weight and volume. An 80lb bag yields about 0.6 cubic feet of concrete, while a 60lb bag yields about 0.45 cubic feet. 80lb bags are more cost-effective for larger jobs but are heavier to lift.
Should I add extra for waste?
Yes, it is standard practice to add 5-10% extra to your order to account for spillage, uneven subgrade, or formwork deflection. Our calculator automatically includes a 5% safety margin in the bag count.
Mark verifies that our volume calculations and yield estimates align with industry standards for residential concrete projects.