18×30 Concrete Slab (6 inches): Yards, Feet & Bags
This 18 ft x 30 ft slab, 6 inches thick, works well for a driveway section or a large patio. Consider whether to use bags or ready-mix based on your site 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)
Always round to 0.25 yd³ when estimating concrete needs to ensure you order enough material.
Ensure your base is well-prepped and forms are sturdy to prevent shifting during pouring.
Apply a smooth finish and keep the surface moist to aid in curing without cracking.
18×30 Slab Thickness Check
For a driveway section, a 6-inch slab fits many heavy load jobs, but subgrade quality, reinforcement, and local requirements still matter.
Current spec
This page estimates a 18×30 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.
driveway section 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 18×30 slab does not settle unevenly.
- Check form height and diagonal measurements before concrete arrives.
- Plan reinforcement, joints, and edge support based on the intended driveway section use.
Worked Example for 18×30 at 6 Inches
Step-by-step calculation for this exact slab:
- Convert thickness to feet: 6 ÷ 12 = 0.5000 ft
- Compute area: 18 × 30 = 540 sq ft
- Volume in cubic feet: 540 × 0.5000 = 270.00 ft³
- Convert to cubic yards: 270.00 ÷ 27 = 10.000 yd³
- Add 10% waste buffer: 10.000 × 1.10 = 11.000 yd³
Concrete Delivery Strategy for 18×30
This slab needs about 10.00 yd³ of concrete, or 450 80 lb bags before waste. With a waste cushion, plan around 11.00 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 18×30
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 | 10.50 | 473 | 630 | 945 |
| +10% typical | 11.00 | 495 | 660 | 990 |
| +15% rough subgrade | 11.50 | 518 | 690 | 1035 |
After the Pour: Timeline for 18×30
For a driveway section, cure time matters more because wheel loads and concentrated weight can punish green concrete too early.
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 18 ft, width 30 ft, thickness 6 in.
Compute Volume
Area: 540 sq ft → volume: 270.0 ft³ → 10.00 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 should I consider when choosing between bags and ready-mix concrete?
Evaluate your project size, site access, and whether you have the means to mix on-site or prefer ready-to-use options.
How do I account for waste when ordering concrete?
It's wise to factor in a buffer for waste, as spills and over-excavation can occur during the pouring process.
What is the best way to prepare the base for my concrete slab?
Ensure the base is compacted and level, with proper drainage to prevent future settling or cracking.
How thick should my concrete slab be for a driveway or patio?
A thickness of inches is generally suitable for heavy loads, but consider the specific use and local conditions.
Related Slab Sizes
Ready to Calculate Your Project?
Get instant estimates for cubic yards, cubic feet, and bag counts. No signup required.