Concrete Volume Calculator
Slab · Column · Footing · Sonotube
4" typical for patios
0.00
cubic yards (with 10% waste)
≈ cubic feet
—
80 lb bags
—
short tons
—
ready-mix trucks
Bag coverage reference
How many bags per cubic yard
| Bag Size | Cu ft / bag | Bags / cu yd | Weight / cu yd |
|---|---|---|---|
| 40 lb | 0.30 | 90 bags | 3,600 lb |
| 60 lb | 0.45 | 60 bags | 3,600 lb |
| 80 lb | 0.60 | 45 bags | 3,600 lb |
| 90 lb | 0.75 | 36 bags | 3,240 lb |
| Ready-mix truck | 216 | — | 8 cu yd |
Frequently asked questions
How many bags of concrete do I need for a 10×10 slab?
For a 10×10 foot slab at 4 inches thick, you need 1.23 cubic yards or approximately 56 bags of 80 lb concrete (with 10% waste factor). At 4 inches thick: 10 × 10 × (4/12) ÷ 27 = 1.23 cu yd × 1.10 = 1.35 cu yd.
How do I calculate concrete for a slab?
Multiply length (ft) × width (ft) × thickness (ft). Convert thickness from inches to feet by dividing by 12. Then divide the total cubic feet by 27 to get cubic yards. Add 10% overage for waste. Formula: (L × W × T/12) ÷ 27 × 1.10
What is the standard slab thickness for a driveway?
Residential driveways should be at least 4 inches thick. If heavy vehicles (SUVs, trucks, RVs) will park on the driveway, use 5–6 inches for improved load capacity and durability.
How much does a yard of concrete weigh?
One cubic yard of concrete weighs approximately 3,600–4,050 pounds (1.8–2 short tons), depending on the mix design, aggregate type, and water content. Standard mixes average about 3,900 lbs per cubic yard.
When should I order ready-mix vs use bags?
For projects over 1 cubic yard (about 45 bags), ready-mix delivery is usually more economical per cubic yard and saves significant labor. For small pours under 0.5 cubic yards, bags from a home improvement store are more practical since minimum delivery charges for ready-mix can be expensive.
How to calculate concrete volume
Calculating concrete volume accurately is the first step in any pour. Too little means stopping mid-project; too much wastes money. The formula varies by shape, but the principle is the same: find the volume in cubic feet, then convert to cubic yards (divide by 27), then add a waste factor.
Concrete slab formula
Volume (cu yd) = Length (ft) × Width (ft) × Thickness (in ÷ 12) ÷ 27
Circular column formula
Volume (cu yd) = π × (Diameter ÷ 2 ÷ 12)² × Height (ft) ÷ 27
Why add a waste factor?
Always order 5–15% more concrete than your calculation shows. Subgrade variations, spillage during placement, and irregular forms all consume extra volume. A standard 10% waste factor is appropriate for most residential projects.