🧱 Concrete Calculator
Enter the length, width and thickness of your slab or footing to get the concrete volume and the number of pre-mix bags to buy.
Concrete volume
0.6 m³
Cubic yards
0.78 yd³
Pre-mix bags
65
incl. ~7% extra
Volume = length × width × thickness. Bags from yield (20 kg bag ≈ 0.01 m³); over-order slightly for structural pours. 🔒 In your browser.
How the concrete calculator works
Concrete volume is length × width × thickness. The tool computes it in cubic metres (or cubic feet/yards), then divides by the yield of a pre-mix bag to estimate the bags needed. A little extra is added because concrete settles and spills, and part-bags round up.
Pre-mix bag yields differ: a 20 kg bag makes roughly 0.009–0.011 m³, an 80 lb bag about 0.6 ft³. For anything structural, over-order slightly — running short mid-pour is far worse than a spare bag.
Frequently asked questions
How do I calculate concrete volume?
Multiply length × width × thickness, all in the same units. A 3 × 2 m slab, 0.1 m thick, is 3 × 2 × 0.1 = 0.6 m³ of concrete.
How many bags of concrete do I need?
Divide the volume by the yield of one bag. If a 20 kg bag yields about 0.01 m³, a 0.6 m³ slab needs roughly 60 bags — so for large pours, ready-mix delivery is usually cheaper.
How much extra concrete should I order?
Add about 5–10%: concrete settles, spills and sub-grades are rarely perfectly level. Running out during a pour creates a weak cold joint, so it’s better to have a little spare.
What thickness should a slab be?
It depends on the load — commonly 100 mm (4 in) for paths and patios, more for driveways or structural slabs. Follow local building guidance for load-bearing work.
Does this handle footings and columns?
Yes for rectangular shapes — enter the length, width and depth. For round columns, multiply π × radius² × height separately.
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