How Much Concrete Do I Need?
Calculate the exact amount of concrete for slabs, footings, walls, and columns. Get results in cubic yards and number of bags with cost estimates.
Quick Answer
A 10×12 ft patio slab at 4 inches thick needs about 1.48 cubic yards of concrete (~67 bags of 80-lb mix), costing roughly $170–$245.
Enter your dimensions above to calculate concrete needed.
💡 1 cubic yard of concrete covers approximately 81 sq ft at 4 inches thick
How to Calculate Concrete Needed
Formula
Length (ft) × Width (ft) × Thickness (in) ÷ 324 = Cubic Yards
Multiply your slab's length by width to get square footage. Multiply by thickness in inches, then divide by 324 to convert to cubic yards.
Example
For a 10 ft × 12 ft patio slab at 4 inches thick: 10 × 12 × 4 ÷ 324 = 1.48 cubic yards. That's about 67 bags of 80-lb concrete mix.
Tips & Best Practices
- •Order 5–10% extra concrete to account for spillage, uneven ground, and forms.
- •Standard slab thickness is 4 inches. Driveways should be 5–6 inches.
- •One 80-lb bag of concrete mix yields about 0.6 cubic feet. You need 45 bags per cubic yard.
- •For projects over 1 cubic yard, consider ordering ready-mix delivery instead of mixing bags.
Quick Reference
1 cubic yard of concrete covers approximately 81 sq ft at 4 inches thick
How Many Bags of Concrete Do I Need?
You need approximately 45 bags of 80-lb concrete mix per cubic yard, or about 60 bags of 60-lb mix per cubic yard.
The table below shows how many bags you need for common slab sizes at 4 inches thick — the standard for patios and walkways.
| Slab Size | Cubic Yards | 80-lb Bags | Est. Cost |
|---|---|---|---|
| 4×4 ft | 0.20 yd³ | ~9 bags | $27–$45 |
| 8×10 ft | 0.99 yd³ | ~45 bags | $114–$163 |
| 10×12 ft | 1.48 yd³ | ~67 bags | $170–$244 |
| 12×20 ft | 2.96 yd³ | ~133 bags | $340–$489 |
| 20×24 ft (2-car garage) | 5.93 yd³ | ~267 bags | $682–$978 |
For projects over 1 cubic yard, ready-mix delivery is usually cheaper and faster than mixing bags by hand.
How Thick Should a Concrete Slab Be?
Standard concrete slab thickness is 4 inches for patios and walkways. Driveways need 5–6 inches. Garage floors should be at least 6 inches thick.
Choosing the right thickness prevents cracking and ensures your slab handles the load it needs to support.
Patios & Walkways — 4 inches
Foot traffic only. A 4-inch slab on a compacted gravel base is the standard for residential patios, sidewalks, and pool decks.
Driveways — 5–6 inches
Must support vehicle weight. Use 5 inches for cars and 6 inches if trucks or RVs will park on it. Reinforce with rebar or wire mesh.
Garage Floors — 6 inches
Heavy loads and potential equipment. A 6-inch slab with wire mesh provides durability for workshops and vehicle storage.
Shed Pads — 4 inches
A 4-inch slab works for most storage sheds. Extend the slab 2–4 inches beyond the shed footprint on each side.
How Much Does Concrete Cost?
Ready-mix concrete costs $115–$165 per cubic yard delivered. Bagged concrete mix costs $3–$5 per 80-lb bag, or roughly $135–$225 per cubic yard mixed yourself.
The total cost of a concrete project depends on slab size, thickness, and whether you DIY or hire a contractor.
| Project | Size | DIY Cost | Pro Installed |
|---|---|---|---|
| Small patio | 8×10 ft | $114–$163 | $640–$1,200 |
| Large patio | 12×16 ft | $256–$368 | $1,150–$2,300 |
| Driveway | 12×40 ft | $682–$978 | $2,900–$5,760 |
| Garage floor | 20×24 ft | $910–$1,305 | $3,840–$7,200 |
Full pricing breakdown: Concrete Slab Cost: What to Expect →
Frequently Asked Questions
How much does a cubic yard of concrete cost?+
Ready-mix concrete costs $115–$165 per cubic yard delivered. Bagged concrete (mixing yourself) runs about $3–$5 per 80-lb bag, or roughly $135–$225 per cubic yard.
How many bags of concrete do I need?+
You need approximately 45 bags of 80-lb concrete mix per cubic yard, or about 60 bags of 60-lb mix per cubic yard.
How thick should a concrete slab be?+
Standard patios and walkways: 4 inches. Driveways: 5–6 inches. Garage floors: 6 inches. Always check local building codes for requirements.
How long does concrete take to cure?+
Concrete reaches about 70% strength in 7 days and full strength in 28 days. You can walk on it after 24–48 hours and drive on it after 7 days.