Concrete Slab Estimator
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Standard patio: 4″, Driveway: 6″
Recommended: 5-10%
Total Volume (Cubic Yards):
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Total Volume (Cubic Feet):
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Est. 80lb Premix Bags:
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Est. 60lb Premix Bags:
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How to Estimate Concrete for a Slab
Calculating the correct amount of concrete is crucial for any construction project, whether you are pouring a patio, a driveway, or a shed foundation. Ordering too little can result in a "cold joint" which weakens the structure, while ordering too much is a waste of money.
The Concrete Formula
To determine the volume of concrete needed, you must calculate the cubic footage of the slab and then convert that into cubic yards (which is how ready-mix trucks measure volume) or the number of pre-mix bags.
The basic formula is:
- Volume (cu. ft.) = Length (ft) × Width (ft) × Thickness (ft)
- Volume (cu. yards) = Volume (cu. ft.) / 27
Note: Since thickness is usually measured in inches, you must divide the inches by 12 to get the foot equivalent before multiplying.
Thickness Guidelines
The thickness of your slab depends on its intended use:
- 4 Inches: Standard for walkways, patios, and residential floor slabs.
- 5-6 Inches: Recommended for driveways and areas holding heavier vehicles.
- 8+ Inches: Heavy-duty commercial aprons or foundations supporting significant weight.
Pre-Mix Bags vs. Ready-Mix Truck
If your project requires less than 1 to 1.5 cubic yards of concrete, it is often more economical to buy pre-mix bags (60lb or 80lb) from a hardware store. For projects requiring 2 cubic yards or more, scheduling a ready-mix truck delivery is usually the better option to ensure consistency and save labor.