Slab cost estimate
20x24 Concrete Slab Cost
A 20 ft × 24 ft concrete slab is 480 square feet. At a standard 4-inch thickness it needs about 6.52 cubic yards of concrete (with 10 % waste) and costs roughly $2,880 – $6,240 installed with a plain broom finish.
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Material & Cost Breakdown
| Metric | Value | Notes |
|---|---|---|
| Square footage | 480 sq ft | 20 ft × 24 ft |
| Thickness | 4 in | Standard residential |
| Concrete volume | 5.93 yd³ | Before waste |
| Order volume (10% waste) | 6.52 yd³ | Ready-mix ordering target |
| 80 lb bags needed | 294 bags | Including waste |
| 60 lb bags needed | 392 bags | Including waste |
| Ready-mix material cost | $847 – $1,076 | ~$130–$165 per yard delivered |
| Installed cost (broom) | $2,880 – $6,240 | $6–$13 per sq ft |
* Installed cost assumes a standard broom finish, easy site access, and a prepared sub-base. Decorative finishes, tear-out, poor soil, or pump-truck access will move the price higher.
20x24 Slab Cost by Thickness
Thickness is the single biggest lever on how much concrete a 20x24 slab needs. A 4-inch pour suits patios and light foot traffic; step up to 5–6 inches for driveways, garages, shops, and anything carrying vehicles or heavy equipment. Each extra inch adds concrete volume and a little labor.
| Thickness | Concrete (10% waste) | Installed cost | Typical use |
|---|---|---|---|
| 4 in (standard) | 6.52 yd³ | $2,880 – $6,240 | Patios, walkways, light foot traffic |
| 5 in | 8.15 yd³ | $3,168 – $6,528 | Driveways, standard garages |
| 6 in | 9.78 yd³ | $3,456 – $6,816 | Shops, RV pads, heavy equipment |
How We Calculated It
- Area: 20 ft × 24 ft = 480 sq ft
- Volume: 480 sq ft × (4 in ÷ 12) = 160.0 cu ft ÷ 27 = 5.93 yd³
- With 10% waste: 5.93 × 1.10 = 6.52 yd³
- Bags (80 lb): 6.52 × 27 ÷ 0.60 cu ft/bag ≈ 294 bags
FAQs
How much does a 20x24 concrete slab cost?
A 20x24 (480 sq ft) concrete slab costs roughly $2,880 to $6,240 installed with a broom finish in 2026. Decorative finishes, tear-out, and site prep can raise the price.
How many cubic yards for a 20x24 slab?
At 4 inches thick, a 20x24 slab needs about 5.93 cubic yards before waste and 6.52 yards after a 10% ordering allowance.
How many 80 lb bags for a 20x24 slab?
You would need about 294 bags of 80 lb concrete (including 10% waste). Above roughly one cubic yard, ready-mix is usually cheaper and easier than bags.
How much does a 20x24 slab cost at 6 inches thick?
A 6-inch 20x24 slab needs about 9.78 cubic yards of concrete and typically runs $3,456 to $6,816 installed. The thicker pour adds concrete volume, so it costs more than the standard 4-inch slab but resists cracking under vehicles and heavy loads.
Planning Your 20x24 Pour
When preparing to pour a 20 ft × 24 ft concrete slab, proper planning is essential to keep your project on budget. The dimensions directly determine the total square footage, which in turn dictates the amount of labor, forming materials, and finishing time required.
The thickness is equally important. While 4 inches is standard for this type of slab, increasing the thickness by just one inch will significantly increase the total cubic yards of concrete needed. Always ensure your sub-base is properly compacted and leveled; an uneven base can lead to thick spots that consume more concrete than your initial estimate predicted. Lastly, ordering with a 10% waste margin is a standard industry practice to account for minor spills, uneven ground, and the small amount of concrete left inside the delivery truck.