18×20 Concrete Slab (6 inches): Yards, Feet & Bags
This 18 ft x 20 ft slab is perfect for a patio or gazebo base. Decide between bagged concrete or ready-mix based on your access and volume needs.
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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)
Always round to 0.25 yd³ when ordering and check yield on the label for accurate quantities.
Ensure your base is well-prepared and forms are secure, especially for thickened edges to prevent shifting.
Apply a smooth finish and keep the surface damp to allow for proper curing without cracking.
How to Estimate This Slab in 3 Steps
Measure
Length 18 ft, width 20 ft, thickness 6 in.
Compute Volume
Area: 360 sq ft → volume: 180.0 ft³ → 6.67 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 should I consider when choosing between bags and ready-mix concrete?
Consider your project's scale, access to the site, and whether you have the means to mix on-site or prefer delivered ready-mix.
How do I determine the right thickness for my slab?
The thickness should be based on the intended use; heavier loads may require greater thickness for stability.
What is the best way to prepare the base for my concrete slab?
Excavate to a suitable depth, ensuring it's level and compacted to prevent settling after pouring.
How can I minimize waste when ordering concrete?
Estimate your needs carefully and add a buffer for spills or over-excavation, rounding your order up as necessary.
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