18×18 Concrete Slab (4 inches): Yards, Feet & Bags
An 18 ft x 18 ft concrete slab at 4 inches thick works well for a patio or gazebo base. Decide between bags or ready-mix based on your 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 your order to ensure you have enough material.
Ensure your base is well-prepared and forms are correctly set up to avoid issues with thickened edges.
After finishing, keep the surface moist and protected to promote a strong cure over time.
How to Estimate This Slab in 3 Steps
Measure
Length 18 ft, width 18 ft, thickness 4 in.
Compute Volume
Area: 324 sq ft → volume: 108.0 ft³ → 4.00 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
Should I use bags or ready-mix concrete for my slab?
Consider ready-mix for larger slabs to save time and labor, while bags can be more convenient for smaller projects.
How much waste should I account for when ordering concrete?
Plan for a buffer to cover spills, over-excavation, or miscalculations, as this can help avoid running short.
What is the best way to prepare the base for my concrete slab?
Excavate to a suitable depth, level the ground, and compact the soil to create a stable foundation.
What thickness should I choose for my concrete slab?
A thickness of inches is common for patios and walkways, balancing strength and material efficiency.
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