How much concrete do I need for a slab? Calculate cubic yards, bags, and costs for patios, driveways, garage floors, and sidewalks. Enter dimensions for instant estimates.
Slab Details
10% recommended for uneven ground and spillage
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Last updated March 2026 by our expert review team
Ready-mix delivery prices. Bags cost more per yard but work for small pours under 1 cu yd.
Ehsan Ghazanfari
Licensed Structural Engineer
FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
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Certified Cost & Estimating Professional
AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.
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How we verify our calculatorsOrder 10% extra concrete. You can't stop a pour to get more, and a short load means a cold joint that weakens the slab permanently.
For slabs over 2 cubic yards, order ready-mix instead of bags. A 10x10x4" slab takes about 50 bags (80lb) vs. one quick pour from a truck. Use our concrete bags calculator for small pours.
Need to know the weight? Our concrete weight calculator converts volume to lbs, tons, and kg for transport and structural planning.
Place control joints every 8 to 10 feet in each direction. Without them, the slab will crack randomly. Cut joints to one-quarter the slab thickness.
Cure concrete for at least 7 days by keeping it moist. Cover with plastic sheeting or spray with curing compound. Proper curing adds 50% to final strength.
For driveways, use 4,000 PSI concrete minimum with 6-inch thickness. Standard 3,000 PSI at 4 inches is fine for patios and walkways.
Need exact rebar quantities? Our concrete rebar calculator estimates sticks, linear feet, and weight by bar size and spacing.
For patio-specific estimates with finish options, use our concrete patio calculator.
Use our concrete cost calculator for a detailed breakdown of material, labor, and finishing costs.
Building a pool? Use our pool volume calculator to estimate water volume, fill time, and chemical needs.
Grade the sub-base with compacted gravel before pouring. 4 inches of crushed stone provides drainage and prevents frost heave. Our crusher run calculator estimates base material.
Enter the slab length, width, and thickness. Select concrete type and waste factor.
The calculator converts thickness to feet, computes volume, and applies the waste factor.
Get cubic yards, bag counts (60lb and 80lb), trucks needed, rebar length, wire mesh sheets, and cost range.
Formulas
Volume = Length x Width x Thickness (in feet)
Cubic Yards = Cubic Feet / 27
Bags (80lb) = Cubic Feet / 0.6
How many bags of concrete for a 10x10 slab?
A 10x10 slab at 4 inches thick needs about 1.23 cu yd or 56 bags of 80lb concrete. With 10% waste, order 62 bags.
How thick should a concrete slab be?
4 inches for patios, walkways, and shed floors. 6 inches for driveways and garage floors. 8 inches for heavy equipment pads.
Do I need rebar or wire mesh?
Wire mesh (6x6 W1.4) is standard for 4-inch slabs. Use #4 rebar on 12-inch centers for driveways, garage floors, and any slab over 5 inches thick.
How much does a concrete slab cost?
$125 to $250 per cubic yard for ready-mix depending on type. A 20x10 patio at 4 inches costs roughly $100 to $200 in concrete alone.
When should I use ready-mix vs. bags?
Use bags for pours under 1 cubic yard (about 45 bags of 80lb). Above that, ready-mix is faster, cheaper per yard, and gives a more consistent mix.
How long does concrete take to cure?
24 to 48 hours for foot traffic, 7 days for vehicle traffic, 28 days for full strength. Keep the surface moist during curing.
Can I pour concrete in cold weather?
Not below 40 degrees F without precautions. Use hot water in the mix, insulating blankets, and avoid freezing for 48 hours. Cold pours below 25 degrees F will fail.
What is a cold joint and how do I avoid it?
A cold joint forms when fresh concrete meets partially cured concrete. Avoid by pouring continuously, having enough help, and ordering enough material to finish without stopping.
A standard backyard patio. Budget $185 to $225 for standard ready-mix concrete.
Two-car driveway section. Use high-strength 4,000 PSI mix. Budget $615 to $735.
Full two-car garage. Requires rebar on 12" centers. Budget $1,325 to $1,590.
Front walkway. Control joints every 4 feet for a clean look. Budget $245 to $295.
Ordering the exact amount
Always add 10% for waste, uneven ground, and spillage. Running short mid-pour creates a cold joint that permanently weakens the slab.
Pouring on bare dirt
You need 4 inches of compacted gravel base for drainage. Without it, water collects under the slab, freezes in winter, and causes heaving and cracking.
Skipping control joints
Concrete will crack. Control joints every 8 to 10 feet give it a place to crack in a straight line instead of randomly across the surface.
Not curing properly
Letting concrete dry too fast leaves a weak surface that dusts and flakes. Keep it moist for 7 days with plastic sheeting or curing compound.
Using wrong thickness for the application
A 4-inch driveway will crack under vehicle weight within a year. Driveways and garage floors need 6 inches minimum with reinforcement.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.