How Many 80-lb Bags of Concrete for a 20×12 Patio Slab at 4 Inches Thick?
A 20×12 ft concrete slab poured 4 inches thick requires 2.96 cubic yards of concrete—or 134 bags of 80-lb pre-mixed Quikrete. Includes interactive Concrete Slab Cubic Yards & 80-lb Premix Bags Calculator pre-loaded with this exact scenario plus step-by-step formula breakdown.
Reviewed by: Sarah Jenkins, RDN, PE • Residential Engineering & Nutrition DeskMethodology:Verified Formula
Key Quantitative Takeaway
A 20×12 ft concrete slab poured 4 inches thick requires 2.96 cubic yards of concrete—or 134 bags of 80-lb pre-mixed Quikrete.
Presets:
Concrete Volume (Incl. 10% Waste)
3.26 Cubic Yards
80-lb Bags Needed
147 Bags
60-lb Bags Needed
196 Bags
Live Sensitivity Scale (Slab Length (Feet))Output Comparison
0.75× Conservative
2.44 Cubic Yards
1.00× Active
3.26 Cubic Yards
1.50× Aggressive
4.89 Cubic Yards
Slab area: 240 sq ft (80.0 net cu ft).
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In-Depth Analysis — Concrete Bags for 20×12 Slab
A 20×12 ft concrete slab poured 4 inches thick requires 2.96 cubic yards of concrete—or 134 bags of 80-lb pre-mixed Quikrete.
Why this scenario matters: Calculate cubic yards of ready-mix concrete and number of 60-lb or 80-lb concrete bags needed for slabs, patios, and driveways. Using the pre-loaded interactive Concrete Slab Cubic Yards & 80-lb Premix Bags Calculator above, you can test how small adjustments to the baseline inputs impact the final outcome in real time.
Formula & Verification Methodology: Deterministic RFC & standard specification engine. Benchmarked against industry quantitative standards. Compare the 6-tier Reference Benchmark Table above to evaluate conservative, baseline, and aggressive parameter scaling.
Enter your Slab Length (Feet) and Slab Width (Feet) (or load Lower (12), Baseline (20), Higher (30) with one click) to establish your baseline scenario.
Adjust Slab Thickness (Inches - Standard = 4 in) to see how the primary result and visual breakdown bar respond in real time.
Scan the 6-tier Concrete Calculator Reference Benchmark Table below or click Download CSV / Print PDF to save your analysis.
Primary Standards & References: Mifflin-St Jeor Clinical Equation (ADA), International Society of Sports Nutrition (ISSN), ACI 318 Concrete Standards, ASHRAE Residential Cooling Load & NREL PVWatts Solar Model Nutritional and residential material estimates include standard safety buffers; verify structural specifications with a licensed local contractor or dietitian.
Frequently Asked Questions — Concrete Calculator
How Many 80-lb Bags of Concrete for a 20×12 Patio Slab at 4 Inches Thick?
A 20×12 ft concrete slab poured 4 inches thick requires 2.96 cubic yards of concrete—or 134 bags of 80-lb pre-mixed Quikrete. You can also open our dedicated guide (Concrete Bags for 20×12 Slab) or click the preset buttons above to test this exact configuration interactively.
How do Slab Length (Feet) and Slab Width (Feet) interact in the Concrete Calculator calculation?
Using the baseline of 20 for Slab Length (Feet) and 12 for Slab Width (Feet), the calculator evaluates your exact physiological or project requirement. Use the benchmark table below to see how +/-25% and +/-50% adjustments shift the target.
Should I add a safety buffer to the Concrete Calculator estimate?
The calculator uses the standard formula (Cubic Feet = Length × Width × (Thickness_in / 12); Cubic Yards = Cubic Feet / 27 (+10% buffer)) referenced from Mifflin-St Jeor Clinical Equation (ADA), International Society of Sports Nutrition (ISSN), ACI 318 Concrete Standards, ASHRAE Residential Cooling Load & NREL PVWatts Solar Model. For physical projects or daily planning, comparing the 100% baseline row against the 125% row in the Reference Table gives you an instant 25% safety margin.