Concrete Calculator
Get the volume of concrete for a slab or patio, and how many premix bags or cubic yards to order.
Quick answer
Cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27. A 10 × 10 ft slab 4 inches deep needs about 1.23 cubic yards. Laying a gravel base first? Use the gravel calculator.
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- Updated October 2026
Cubic yards
1.36 yd³
- Cubic meters
- 1.04 m³
- Cubic feet
- 36.7 ft³
- 80 lb bags (0.60 ft³ each)
- 62
- 60 lb bags (0.45 ft³ each)
- 82
- 25 kg bags (≈0.012 m³ each)
- 87
Show the working
- 10 × 10 × (4 ÷ 12) × 1.1 = 36.67 ft³
- 36.67 ÷ 27 = 1.36 yd³
About the Concrete calculator
Concrete is ordered by volume — cubic yards in the US, cubic metres elsewhere. For small jobs you’ll buy premixed bags instead; an 80 lb bag yields about 0.60 cubic feet and a 60 lb bag about 0.45 cubic feet once mixed.
Order 5–10% more than the exact volume. Sub-bases are never perfectly flat, forms bow slightly, and running short in the middle of a pour leaves a weak cold joint.
How to use it
- Choose feet/inches or metres/cm.
- Enter the slab length and width.
- Enter the thickness: 4 in (10 cm) for patios and paths, 5–6 in (12–15 cm) for driveways.
- Keep 10% extra unless your base is laser-levelled.
The formula
Volume = Length × Width × Thickness
- Imperial: ft × ft × (in ÷ 12) = cubic feet; ÷ 27 = cubic yards.
- Bags = cubic feet ÷ yield per bag, rounded up.
Worked example
A 10 × 10 ft patio, 4 in thick
- 10 × 10 × (4 ÷ 12) = 33.3 cubic feet.
- 33.3 ÷ 27 = 1.23 cubic yards (before extra).
- With 10% extra: 36.7 cu ft → 62 bags of 80 lb, or about 1.36 yd³ ready-mix.
Frequently asked questions
How many 80 lb bags make a yard of concrete?
About 45 bags (27 cu ft ÷ 0.60). For more than about one cubic yard, ready-mix delivery is usually cheaper and much less work.
How thick should a concrete slab be?
Four inches is standard for patios, walkways and shed bases. Driveways that take cars usually need 5–6 inches, and heavier vehicles more, plus reinforcement.
How long before I can walk or drive on it?
Typically walkable after 24–48 hours and drivable after about 7 days. Concrete reaches its design strength around 28 days.
Results are estimates for planning — check critical figures with a professional or the official source.
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