Concrete Slab Calculator

Pouring a concrete slab requires knowing exactly how much material to order — too little and the job stalls, too much and you're paying for waste. Enter your slab length, width, thickness, and number of slabs into the Concrete Slab Calculator, then select a waste factor to get the concrete volume in cubic yards and cubic feet. Secondary outputs include estimated weight, and the number of 60lb and 80lb bags needed — with optional hole/cutout deductions if your slab has openings.

ft
ft
in
ft

Diameter of circular holes to subtract

in

Add extra concrete for waste and spillage

Results

Concrete Volume Needed

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Volume in Cubic Feet

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Estimated Weight

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60lb Bags Needed

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80lb Bags Needed

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Frequently Asked Questions

How do I calculate concrete for a slab?

To calculate concrete for a slab, multiply length × width × thickness. Convert thickness from inches to feet by dividing by 12, then divide the result by 27 to get cubic yards. Always add 5-15% extra for waste.

How many 80lb bags of concrete do I need?

An 80lb bag of concrete covers approximately 0.6 cubic feet or 0.022 cubic yards. Divide your total cubic yards by 0.022 to determine the number of 80lb bags needed.

What thickness should my concrete slab be?

Standard concrete slab thickness varies by use: 4 inches for sidewalks and patios, 4-6 inches for driveways and garage floors, and 6+ inches for heavy-duty applications or areas with heavy vehicle traffic.

How much does concrete weigh per cubic yard?

Standard concrete weighs approximately 4,000-4,050 pounds per cubic yard. This can vary slightly depending on the mix design and aggregate type used in the concrete.

Should I order extra concrete?

Yes, always order 5-15% extra concrete to account for waste, spillage, and minor measurement variations. It's better to have slightly too much than to run short during the pour.

Can I use this calculator for footings and walls?

Yes, this calculator works for any rectangular concrete structure. For footings, enter the footing dimensions. For walls, use length × height × thickness to calculate volume.

How do I account for holes or cutouts in my slab?

Enter the diameter and depth of any holes or cutouts in the holes section. The calculator will subtract this volume from your total concrete needs automatically.

What's the difference between cubic feet and cubic yards?

Cubic yards are the standard unit for ordering concrete. One cubic yard equals 27 cubic feet. Most concrete suppliers price and deliver concrete by the cubic yard.