Concrete Calculator
Calculate how much concrete you need for a slab, patio or base in cubic metres or cubic yards, plus the number of 20 kg, 25 kg, 40 lb, 60 lb or 80 lb bags.
Enter your values and press Calculate.
How to use the Concrete calculator
Ready-mix concrete is ordered by the cubic metre (UK, Europe) or cubic yard (US), while bagged premix is sold by weight. A garden path or patio base is usually 10 cm (4″) thick; driveways 15 cm (6″).
Always order a little extra — uneven ground and spillage mean 5–10% more than the exact volume is normal.
Formula
Volume = length × width × thickness (all in the same unit). 1 yd³ = 27 ft³ = 0.7646 m³.
Bag counts use typical premix yields: an 80 lb bag makes about 0.60 cu ft, a 60 lb bag 0.45 cu ft and a 40 lb bag 0.30 cu ft. Metric bags assume about 2,150 kg of dry mix per m³ of concrete.
Frequently asked questions
How much concrete do I need for a 3 m × 3 m slab?
At 10 cm thick, 0.9 m³ — about 1 m³ with 10% extra.
How much does a cubic yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches thick.