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Concrete Slab Calculator

Result
—cubic yards
◆ LIVE 3D PREVIEW
Bags (60-lb)
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Est. Cost
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How to Calculate Concrete for a Slab

Multiply Length × Width × (Thickness÷12) to get cubic feet. Divide by 27 to get cubic yards. Add 10% for waste.

How Much Does Concrete Cost?

Ready-mix: $115–$150/cubic yard delivered. Bags: $4.50–$5.50 per 60-lb bag. A 20×15ft slab (4in thick) costs ~$285–$370.

Common Slab Thicknesses

Sidewalk: 4in • Patio: 4in • Driveway: 5–6in • Garage: 6in • Foundation: 8–12in

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CalcBuild › Concrete Slab Calculator

How to Calculate Concrete Slab

Use this free concrete slab calculator to get instant, accurate results for your construction project. Simply enter your measurements above and the calculator will automatically compute the result using industry-standard formulas.

Pro Tip: Always add 10-15% extra material to account for waste, cuts, and job-site conditions. This is standard practice recommended by experienced contractors.

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💡 Pro Tips — Concrete Slab

📊 Coverage Reference Table

ThicknessSq Ft per Yard80-lb Bags per 100 sqft
3"108~14
4"81~19
5"65~24
6"54~28
8"40~38

❓ Frequently Asked Questions

+How much does a yard of concrete cover?
One cubic yard covers 81 sq ft at 4" thick, 54 sq ft at 6" thick, or 27 sq ft at 12" thick. Always order 10% extra.
+How many 80-lb bags make a cubic yard?
Approximately 45 bags of 80-lb concrete. For 60-lb bags, you need about 60. For 40-lb bags, about 90.
+How long does concrete take to cure?
Walk-on strength in 24-48 hours. Park a car after 7 days. Full structural strength at 28 days. Keep wet for the first 7 days for best results.
+Should I use rebar or wire mesh?
Wire mesh works for standard 4" patios. Use #4 rebar at 18" spacing for driveways, garages, or anything carrying vehicle weight.
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