Concrete Calculator
Free concrete calculator for slabs, pads and patios. Get cubic yards, cubic metres and the number of 40, 60 or 80 lb bags, in imperial or metric.
How it works
Volume = length × width × thickness × (1 + waste %). Cubic yards = cubic feet ÷ 27. Cubic metres = cubic feet × 0.0283168. Bags assume typical premix yields of about 0.60 ft³ (80 lb), 0.45 ft³ (60 lb) and 0.30 ft³ (40 lb); check the yield printed on your bag.
Examples
- A 10 ft × 10 ft slab, 4 in thick = 33.33 ft³ = 1.23 yd³ (0.94 m³), about 56 × 80 lb bags before waste.
- A 3 m × 3 m × 10 cm pad = 0.9 m³ (1.18 yd³).
FAQ
How thick should a concrete slab be?
Patios and walkways are commonly 4 in (10 cm); driveways are often 5–6 in. Follow local code and your engineer for structural work.
Should I order extra concrete?
Most people add 5–10% for spillage, uneven subgrade and form flex.
Bags or ready-mix?
Bags make sense for small jobs; above roughly 1 yd³ (0.75 m³) ready-mix delivery is usually easier.