18×20 Concrete Slab (4 inches): Yards, Feet & Bags
An 18 ft x 20 ft concrete slab is perfect for a patio or gazebo base. Decide between using bags or ready-mix based on access and waste factor.
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Quick Answer
Tip: Always confirm the yield printed on your bag label. Bag yield guide
Large pour: consider ready-mix delivery for speed and consistent results. Bag counts this high can take significant mixing time.
Project Notes (Unique)
Check yield on the label and round to 0.25 yd³ for accurate ordering.
Ensure your base is well-prepped and forms are set correctly to avoid issues with thickened edges.
Finish the surface as desired and allow it to cure properly before heavy use.
How to Estimate This Slab in 3 Steps
Measure
Length 18 ft, width 20 ft, thickness 4 in.
Compute Volume
Area: 360 sq ft → volume: 120.0 ft³ → 4.44 yd³.
Add Waste
Add a small buffer for spillage and uneven subgrade, then round up when ordering.
Planning Notes
Common uses: patio, gazebo base, walkway section.
For more context and conversions, see the Concrete Calculator hub.
Frequently Asked Questions
What’s better for my project, bags or ready-mix concrete?
Bags offer flexibility for small projects, while ready-mix is efficient for larger areas, saving time and labor.
How much extra concrete should I plan for?
Always consider a waste factor to cover spills, over-excavation, or adjustments during pouring.
What should I consider for base preparation?
A solid, level base is critical; ensure it’s compacted and free of debris to support the slab properly.
How thick should my concrete slab be?
A thickness of inches is generally suitable for patios and walkways, but consider additional thickness for heavier structures.
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