The Formula
Concrete volume is measured in cubic yards. The math is the same whether you're pouring a small patio or a full driveway slab — just convert your thickness to feet first.
A 10 × 10 ft patio at 4 inches thick: 10 × 10 × 0.333 ÷ 27 = 1.23 cubic yards. Add 10% waste and you're ordering 1.35 yards — round up to 1.5 for the ready-mix minimum.
Don't want to do the arithmetic? The concrete calculator handles it instantly — cubic yards, bags, and cost in one step.
Concrete Volumes for Common Projects
Ready-to-use estimates for the most common residential pours at standard thicknesses. All include a 10% waste buffer.
| Project | Dimensions | Thickness | Cubic yards (+ 10%) |
|---|---|---|---|
| Small patio | 10 × 10 ft | 4 in | 1.4 yd³ |
| Medium patio | 12 × 16 ft | 4 in | 2.6 yd³ |
| Sidewalk / path | 4 × 40 ft | 4 in | 2.2 yd³ |
| Single-car garage floor | 12 × 22 ft | 4 in | 3.6 yd³ |
| Single-car driveway | 10 × 20 ft | 5 in | 3.4 yd³ |
| Two-car driveway | 20 × 40 ft | 6 in | 16.3 yd³ |
How Thick Should Your Slab Be?
Thickness is the single biggest driver of your concrete volume — and the number most homeowners underestimate. Too thin and the slab cracks under load; thicker costs more upfront but pays for itself in longevity.
| Use case | Recommended thickness |
|---|---|
| Foot traffic only (path, patio, pool deck) | 4 inches |
| Light vehicles (occasional passenger car) | 4–5 inches |
| Standard residential driveway | 5–6 inches |
| Heavy vehicles (trucks, RVs, repeated loads) | 6–8 inches |
| Structural floor slab (per engineer spec) | 6 inches + |
For most residential slabs, a 4-inch compacted gravel base under the concrete is worth the extra effort — it improves drainage, reduces cracking, and gives the slab a stable platform. On clay-heavy or soft soil, go 6 inches of base.
Bags vs. Ready-Mix: Which Should You Order?
This decision comes down almost entirely to volume. There's a fairly clear crossover point.
Use bags when...
Your project is under about 1 cubic yard — think a post footing, a small set of steps, or a 6 × 6 ft pad. Bags are available at any hardware store, require no delivery window, and you mix exactly what you need. The downside: hand-mixing is slow and labor-intensive, and bags cost significantly more per cubic yard than ready-mix.
A 60 lb bag yields 0.45 cubic feet. An 80 lb bag yields 0.60 cubic feet. Since one cubic yard equals 27 cubic feet, filling a single yard takes roughly 60 bags at 60 lb, or 45 bags at 80 lb.
Use ready-mix when...
Your project hits 1 cubic yard or more. A ready-mix truck delivers concrete already mixed to your specified PSI — you just place and finish it. Much faster for large pours, and consistency is far better than hand-mixing. Watch for short-load fees: most suppliers charge $100–$200 extra if you order less than the truck minimum (typically 5–7 cubic yards). If your job falls in the 1–5 yard range, call a few suppliers and compare short-load policies before committing.
Which PSI Do You Need?
PSI is the compressive strength of cured concrete — how much load it can bear per square inch. Higher PSI costs a bit more per yard but is rarely worth skimping on for exterior slabs.
| PSI rating | Best for |
|---|---|
| 2,500 PSI | Interior floors, low-traffic patios, mild climates |
| 3,000 PSI | Standard residential driveways, patios, most exterior slabs |
| 4,000 PSI | Heavy driveways, freeze-thaw climates, high-traffic areas |
| 5,000 PSI + | Commercial, structural, heavy equipment — usually engineer-specified |
For most residential driveways and patios, 3,000 PSI is the sweet spot. If you're in a climate with harsh winter freeze-thaw cycles, step up to 4,000 PSI — the denser mix resists water infiltration and surface spalling significantly better over time.
Cost Estimate
Concrete pricing swings significantly by region and supplier. These ranges give you a realistic starting point — always get at least two local quotes.
A standard 2-car driveway (20 × 40 ft, 6 inches deep) needs about 16 cubic yards. At $175/yard, that's roughly $2,800 just for concrete — before forming, finishing, or labor. For a 10 × 10 patio at 4 inches, expect about $220–$280 in bags from a hardware store, or $400–$500 ready-mix including a short-load fee. Contractor labor typically adds $3–$10 per square foot depending on finish and market.
Before You Pour — Checklist
- Add 10% for waste. Concrete spreads unpredictably, sticks to equipment, and uneven subgrade eats volume faster than expected. Always order slightly more than your raw calculation.
- Compact the subgrade first. Soft or disturbed soil causes settling and cracking. Run a plate compactor over the base before pouring — or add 4–6 inches of compacted gravel on top of any soft ground.
- Set forms before calling the truck. Ready-mix has a working window of roughly 60–90 minutes from the time it leaves the plant. Have your forms built, rebar placed, and crew ready before the truck arrives.
- Plan for rebar or wire mesh. Unreinforced concrete cracks. A grid of #3 or #4 rebar on 18-inch centers, or 6×6 wire mesh, dramatically extends slab life — especially for driveways that take vehicle load.
- Ask about short-load fees upfront. Ordering less than the truck minimum (usually 5–7 yards) triggers a surcharge. Get the exact fee in writing before you commit to a supplier.
- Cut control joints on large slabs. For any slab bigger than about 10 × 10 ft, cut or trowel control joints every 8–10 feet in both directions. They guide cracking so it happens along straight lines, not randomly across the middle of your slab.
- Respect the cure window. Foot traffic: 24–48 hours. Vehicles: 7 days minimum. Full design strength: 28 days. Parking on fresh concrete too soon is one of the most common causes of premature cracking.
Common Questions
How many bags of concrete for a 10 × 10 slab?
At 4 inches thick, a 10 × 10 ft slab is about 33.3 cubic feet. Using 80 lb bags (0.60 ft³ each), you need about 56 bags. Using 60 lb bags (0.45 ft³ each), that's about 74 bags. Add 10% for waste: 62 or 82 bags respectively. At this volume, renting a mixer or calling a ready-mix supplier for a small load is seriously worth considering — mixing 60+ bags by hand is exhausting.
How thick should a concrete driveway be?
4–5 inches is the minimum for a standard residential driveway — but 6 inches is the smarter choice if you park trucks, SUVs, or anything heavy, or if you're in a freeze-thaw climate. Thicker slabs cost more upfront but crack far less over time. Check your local building code before starting permitted work — some municipalities specify a minimum thickness for driveways.
How long does concrete take to cure?
Concrete reaches initial set in 24–48 hours — enough for careful foot traffic. By 7 days it's at roughly 70% of its design strength, and engineers measure its rated PSI at the full 28-day cure. Keep vehicles off the slab for at least 7 days, ideally 10–14. In cold weather, curing slows significantly — protect fresh concrete from freezing with insulated blankets and expect a longer wait before use.
Can I pour concrete in sections?
Yes — large slabs are often poured in sections with intentional cold joints between them. Plan your pour breaks to align with your control joint layout (every 8–10 ft) so the divisions look intentional. Let the first section cure at least 24 hours before pouring adjacent to it, and apply a concrete bonding agent to the cold joint face if structural continuity matters.