Free Tool
Free concrete slab calculator
Enter your slab length, width, and thickness and get cubic yards, cubic feet, and bag counts, plus form boards and a rebar grid when you need them. Order the right amount the first time. Free, no signup.
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Pour the slab once, order it right
A slab is the easy shape to measure and the easy one to come up short on. Enter length and width in feet and thickness in inches, and the calculator gives you cubic yards, which is what the ready-mix plant wants to hear.
Thickness is where the volume hides. Going from a four inch slab to a five inch slab is twenty five percent more concrete on the same footprint, so double check the number before you order.
Turn on rebar and set your grid spacing to get the total linear feet and how many twenty foot sticks that works out to. The form boards line gives you the perimeter footage for your edge forms.
The waste allowance covers subgrade that is never perfectly flat and forms that flex under the load. Ten percent is a fair starting point, and rough ground earns a little more.
Concrete Slab Calculator questions
How much concrete do I need for a slab?
Multiply length by width by thickness, convert to cubic yards, and add waste. The calculator does all of it and shows the yards to order.
How thick should a slab be?
Four inches suits most patios and walkways. Driveways and anything carrying vehicles usually go five to six. Confirm against your local code and the load.
How much rebar for a slab?
It depends on your grid spacing. Turn on the rebar option, set the spacing, and the calculator returns the total linear feet and the number of twenty foot sticks.
Is this really free?
Yes. No email, no signup, and nothing you type leaves your browser.
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Disclaimer: These free tools and templates are provided for general information and estimating purposes only. All results — including quantities, material and cost estimates, load, sizing, and span figures, scores, and any guidance or warnings — are rough approximations that may not fit your specific project, site conditions, local building codes, or current prices. They are not engineering, architectural, structural, legal, financial, or other professional advice, and are not a substitute for a licensed engineer, architect, contractor, or other qualified professional. Always confirm quantities, sizing, and structural, electrical, mechanical, and code requirements with a licensed professional and your local authority having jurisdiction before purchasing materials or performing any work. Werx makes no warranty as to accuracy and accepts no liability for any decision made using these tools. Use at your own risk. See our Terms of Service.