How much concrete do I need for a 10x10 slab?
A 10 ft × 10 ft slab at 4 in thick needs 33.3 cubic feet, or 1.23 cubic yards, before waste. Add 10% for a practical order of about 1.36 cubic yards.
Slab calculator
Concrete Slab Calculator
Work out how much concrete a slab needs in cubic yards, cubic metres, 50/60/80 lb bags and cost. Enter the length, width and thickness, then add a waste allowance for the pour.
Last updated:
How to calculate concrete for a slab
Slab volume = length × width × thickness. Convert the thickness from inches to feet by dividing by 12, multiply all three dimensions, then divide the cubic feet by 27 to get cubic yards.
Example: 10 ft × 10 ft slab at 4 in thick
10 × 10 × (4 ÷ 12) = 33.3 cubic feet. Divide by 27 to get 1.23 cubic yards. Add 10% waste for a practical order of about 1.36 cubic yards, or roughly 64 × 80 lb bags. At $150 per cubic yard, the ready-mix would cost about $204 before delivery.
Common slab sizes at 4 in thick
| Size | Concrete | 80 lb bags* |
|---|---|---|
| 10 ft × 10 ft | 1.23 cu yd | 58 |
| 12 ft × 12 ft | 1.78 cu yd | 84 |
| 20 ft × 20 ft | 4.94 cu yd | 231 |
| 24 ft × 24 ft | 7.11 cu yd | 333 |
| 30 ft × 40 ft | 14.81 cu yd | 693 |
*Before waste. Add 5–10% for spillage and uneven subgrade.
Tips for ordering concrete for a slab
- Add 5–10% waste for spillage, uneven subgrade and over-excavation.
- A 4 in slab suits patios and shed floors; use 5–6 in for driveways and vehicle loads.
- Order ready-mix for anything above about 1 cubic yard; bagged mix is heavier and usually costs more per yard.
- Confirm the subbase, formwork and reinforcement with your supplier or engineer before pouring.
Concrete Slab Calculator FAQ
How many bags of concrete for a 10x10 slab at 4 inches?
At 4 in thick, a 10 ft × 10 ft slab needs about 58 × 80 lb bags before waste, or roughly 64 bags with a 10% allowance. Bag yields vary by brand, so check the yield printed on the bag.
How much concrete for a 20x20 slab?
A 20 ft × 20 ft slab at 4 in thick is 133.3 cubic feet, or 4.94 cubic yards, before waste. Add 10% for a practical order of about 5.43 cubic yards.
How much concrete for a 30x40 slab?
A 30 ft × 40 ft slab at 4 in thick is 400 cubic feet, or 14.81 cubic yards, before waste. Add 10% for about 16.3 cubic yards, which is usually two truckloads from a ready-mix supplier.
How thick should a concrete slab be?
Residential patios and shed floors are commonly 4 in thick. Driveways and slabs that carry vehicles often use 5–6 in. Follow the engineered plan or local building code for the final thickness.
How much does a 10x10 concrete slab cost?
Ready-mix for 1.36 cubic yards typically costs about $165–$245 at $120–$180 per cubic yard, before delivery and short-load fees. Bagged mix often costs more per cubic yard but makes sense for very small pours.
Related calculators