Estimate materials for your next pour
Tip: For slabs, standard thickness is 4 inches for patios and walkways, 6 inches for driveways. Always add 10% extra for waste and spillage.
Whether you're pouring a patio, building a foundation, or setting fence posts, knowing exactly how much concrete you need saves time and money. Our free concrete calculator handles the math for slabs, footings, columns, and stairs — giving you cubic yards, bag counts, and cost estimates in seconds.
To calculate concrete for a slab, multiply the length × width × thickness (all in feet), then divide by 27 to convert cubic feet to cubic yards. For thickness in inches, divide by 12 first.
Example: A 10 ft × 10 ft patio at 4 inches thick = 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.24 cubic yards.
| Project Type | Recommended Thickness | Notes |
|---|---|---|
| Sidewalks & pathways | 4 inches | Light foot traffic only |
| Patios | 4 inches | Standard residential use |
| Driveways | 5–6 inches | Must support vehicle weight |
| Garage floors | 6 inches | Heavy loads, consider rebar |
| Foundations | 8–12 inches | Check local building codes |
If you're mixing concrete yourself, here's how much each bag size covers:
| Bag Size | Yield (cubic feet) | Yield (cubic yards) | Avg. Price |
|---|---|---|---|
| 40 lb bag | 0.30 ft³ | 0.011 yd³ | $3–$5 |
| 60 lb bag | 0.45 ft³ | 0.017 yd³ | $4–$6 |
| 80 lb bag | 0.60 ft³ | 0.022 yd³ | $5–$8 |
For projects over 1 cubic yard, ordering ready-mix concrete delivered by truck is usually more cost-effective than mixing bags by hand.
A 10×10 foot slab at the standard 4-inch thickness requires approximately 1.24 cubic yards of concrete without waste. Adding the recommended 10% waste factor brings it to about 1.36 cubic yards, or roughly 62 bags of 80 lb concrete mix.
It takes approximately 45 bags of 80 lb concrete mix, 59 bags of 60 lb mix, or 91 bags of 40 lb mix to make 1 cubic yard of concrete. For projects requiring more than a yard, ready-mix delivery is usually more practical and economical.
Multiply length (feet) × width (feet) × depth (feet), then divide by 27. If your depth is in inches, divide inches by 12 first to convert to feet. For example: 20 ft × 10 ft × (6 in ÷ 12) = 100 cubic feet ÷ 27 = 3.7 cubic yards.
Ready-mix concrete costs $120–$200 per cubic yard on average, depending on your location, the mix type, and the quantity ordered. Additional costs may include delivery fees ($50–$100), short-load fees for small orders, and pump truck fees ($150–$300) if the truck can't reach the pour site.
For small projects (under 0.5 cubic yards), mixing bags is typically cheaper. For larger projects, ready-mix is almost always more economical. At $6.50 per 80 lb bag, 1 cubic yard of hand-mixed concrete costs about $290 in materials alone — compared to $120–$200 for ready-mix delivered. Plus, mixing 45+ bags by hand is extremely labor-intensive.
A residential concrete driveway should be 5–6 inches thick. If heavy vehicles (RVs, trucks) will use it regularly, go with 6 inches minimum. Use 4,000 PSI concrete mix and add fiber reinforcement or wire mesh for durability. A thicker edge (8 inches) where vehicles enter helps prevent cracking.
Add 10% for standard rectangular pours on level ground. Use 15% for irregularly shaped areas or slightly uneven terrain. For slopes, curves, or complex forms, add 20% or more. It's always better to have a small amount of extra concrete than to run short during a pour.