20×24 Concrete Slab (6 inches): Yards, Feet & Bags
This 20 ft x 24 ft concrete slab, at 6 inches thick, works well for a driveway section or a shop floor. Decide between using bags or ready-mix based on your delivery access and project scale.
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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)
For accurate ordering, round to 0.25 yd³ and check yield on the label to ensure you have enough material.
Ensure your base is well-prepared and forms are sturdy to prevent shifting, especially if you're adding thickened edges.
Apply a smooth finish, and keep the slab moist during curing to enhance strength and durability.
20×24 Slab Thickness Check
A 6-inch slab gives this patio extra stiffness and tolerance if soil conditions are imperfect or loads may grow over time.
Current spec
This page estimates a 20×24 slab poured at 6 inches.
Load check
Best fit depends on whether this is mainly pedestrian use, storage, or heavier wheel traffic.
Upgrade trigger
If you expect heavier loads later, compare this design against the alternate thickness before ordering.
What to Prepare Under a 20×24 Concrete Slab
Most slab problems start below the concrete. Keep the base level, compacted, and consistent before you pour.
- Strip loose topsoil and organic material until you reach firm subgrade.
- Compact the base in lifts so the 20×24 slab does not settle unevenly.
- Check form height and diagonal measurements before concrete arrives.
- Plan reinforcement, joints, and edge support based on the intended patio use.
Worked Example for 20×24 at 6 Inches
Step-by-step calculation for this exact slab:
- Convert thickness to feet: 6 ÷ 12 = 0.5000 ft
- Compute area: 20 × 24 = 480 sq ft
- Volume in cubic feet: 480 × 0.5000 = 240.00 ft³
- Convert to cubic yards: 240.00 ÷ 27 = 8.889 yd³
- Add 10% waste buffer: 8.889 × 1.10 = 9.778 yd³
Bag Mix or Ready-Mix for a 6-inch patio?
This slab needs about 8.89 yd³ of concrete, or 400 80 lb bags before waste. With a waste cushion, plan around 9.78 yd³.
For this volume, ready-mix is usually the safer plan. Round up, confirm delivery minimums, and make sure your crew can place and finish the slab without delays.
Adjust dimensions in the slab calculator or compare bag counts here.
Bag Counts by Waste Buffer for 20×24
Pick a buffer based on site conditions: smooth forms and good subgrade can run leaner; uneven excavation or hard-to-reach pours need more cushion.
| Buffer | Yards (yd³) | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| +5% tight pour | 9.33 | 420 | 560 | 840 |
| +10% typical | 9.78 | 440 | 587 | 880 |
| +15% rough subgrade | 10.22 | 460 | 614 | 920 |
After the Pour: Timeline for 20×24
Protect the slab after finishing, keep the surface from drying too fast, and avoid heavy service until the concrete has had time to gain strength.
First 24 hours
Protect edges, prevent washout, and avoid unnecessary traffic while the slab sets.
Days 2-7
Maintain curing conditions and monitor joints, surface drying, and weather exposure.
Up to 28 days
Concrete keeps gaining strength, so wait for the right service window before heavy use.
How to Estimate This Slab in 3 Steps
Measure
Length 20 ft, width 24 ft, thickness 6 in.
Compute Volume
Area: 480 sq ft → volume: 240.0 ft³ → 8.89 yd³.
Add Waste
Add a small buffer for spillage and uneven subgrade, then round up when ordering.
Planning Notes
Common uses: driveway section, shop floor, large patio.
For more context and conversions, see the Concrete Calculator hub.
Frequently Asked Questions
What is the best option for mixing concrete: bags or ready-mix?
Ready-mix is often more convenient for larger projects, while bags can be useful for smaller areas or DIY jobs.
How do I determine the right thickness for my concrete slab?
Consider the intended use; heavier loads may require a thicker slab for added strength and stability.
What should I do to prepare the base before pouring concrete?
Clear the area of debris, ensure a level surface, and compact the soil to provide a stable foundation for the slab.
How much extra concrete should I order?
It's wise to order a bit more than estimated to account for spillage, over-excavation, or miscalculations.
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