16×20 Concrete Slab (6 inches): Yards, Feet & Bags
This 16 ft x 20 ft slab is perfect for a patio or gazebo base. Decide between bags or ready-mix based on your access and waste factor.
Choose Your Calculator
Slab Calculator
Enter any custom length, width, and thickness to get cubic yards and bag counts.
Open Slab CalculatorBag Calculator
Choose 40/60/80 lb bag sizes and estimate counts for your exact volume.
Open Bag CalculatorWant other sizes? Browse all slab size pages
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 for your chosen concrete mix.
Ensure your base is well-prepared and consider thickened edges for added strength.
Finish your surface as desired and allow for proper curing by keeping it moist and shaded.
How 6-inch Performs on This patio
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 16×20 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.
patio Base Work for a 6-inch 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 16×20 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 16×20 at 6 Inches
Step-by-step calculation for this exact slab:
- Convert thickness to feet: 6 ÷ 12 = 0.5000 ft
- Compute area: 16 × 20 = 320 sq ft
- Volume in cubic feet: 320 × 0.5000 = 160.00 ft³
- Convert to cubic yards: 160.00 ÷ 27 = 5.926 yd³
- Add 10% waste buffer: 5.926 × 1.10 = 6.519 yd³
Order Planning for a 16x20 Concrete Slab
This slab needs about 5.93 yd³ of concrete, or 267 80 lb bags before waste. With a waste cushion, plan around 6.52 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 16×20
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 | 6.22 | 280 | 374 | 560 |
| +10% typical | 6.52 | 294 | 392 | 587 |
| +15% rough subgrade | 6.81 | 307 | 409 | 614 |
Cure Timeline for a 16x20 Concrete Slab
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 16 ft, width 20 ft, thickness 6 in.
Compute Volume
Area: 320 sq ft → volume: 160.0 ft³ → 5.93 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 size, site access, and whether you can handle mixing on-site or prefer a ready-to-use option.
How do I determine the right thickness for my concrete slab?
Thickness depends on the intended use; heavier loads may require a thicker slab for durability.
What are the key steps in preparing the base for my slab?
Clear the area of debris, level the ground, and compact the soil to create a stable foundation.
How can I prevent cracking during the curing process?
Keep the slab moist and covered to protect it from extreme temperatures and direct sunlight.
Related Slab Sizes
Ready to Calculate Your Project?
Get instant estimates for cubic yards, cubic feet, and bag counts. No signup required.