Concrete Slab Calculator
Calculate cubic yards, bags, cost, and rebar for concrete slabs by length, width, and thickness.
How It Works
This calculator is designed specifically for concrete slabs. Enter your slab dimensions and it calculates volume, bag counts, cost, and rebar quantities.
Formula: Cubic Yards = Length (ft) × Width (ft) × Thickness (in) / 12 / 27 × (1 + Waste%).
Bag estimates: One 80 lb bag yields about 0.6 cu ft of mixed concrete. One 60 lb bag yields about 0.45 cu ft. Counts are rounded up.
Rebar: Calculated as a grid at the selected spacing. Total linear feet includes bars running in both directions across the slab.
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
A 10 ft x 10 ft slab at 4 inches thick requires about 1.24 cubic yards of concrete before waste. With a standard 10% waste factor, plan on approximately 1.36 cubic yards. That is about 61 bags of 80 lb concrete mix if you are not ordering ready-mix.
How thick should a concrete slab be?
Standard residential slabs (patios, walkways, shed pads) are 4 inches thick. Driveways should be 5-6 inches. Garage slabs are typically 4-6 inches. For heavy equipment or commercial use, 6-8 inches or more may be needed with engineering review.
Do I need rebar in a concrete slab?
Rebar is recommended for driveways, garage slabs, and any slab over 4 inches thick or subject to heavy loads. For patios and walkways, welded wire mesh (WWM) or fiber reinforcement may be sufficient. Rebar is typically placed on a grid at 12, 16, or 18 inch spacing.
How much does ready-mix concrete cost per yard?
Ready-mix concrete typically costs $130-$160 per cubic yard delivered, depending on your area and the mix design. Short-load fees ($50-$100) may apply for orders under 5-10 yards. Saturday delivery and special mixes (high-strength, fiber) may cost more.
How long does it take for a concrete slab to cure?
Concrete reaches about 70% of its strength in 7 days and full design strength at 28 days. You can walk on it after 24-48 hours and drive on it after 7 days. Avoid heavy loads for at least 28 days. Keep the surface moist for the first 7 days for best results.