Concrete estimating without the guesswork
Concrete math is simple geometry with two traps: mixed units and running short. This calculator handles all three common pours — slabs, footings/trenches and round columns — in one place, takes feet-and-inches or metres-and-centimetres directly (no converting 4 inches to 0.333 ft by hand), and shows the answer three ways at once: cubic feet, cubic yards and cubic metres, since suppliers quote in different units.
The classic example: a 10 × 10 ft patio at 4 inches thick is 33.3 ft³ ≈ 1.23 yd³ of concrete — about 56 bags of 80 lb mix before waste, or 62 bags with the recommended 10% allowance. Bump the thickness to 6 inches (driveway spec) and you need half again as much: 1.85 yd³.
Always order more than the geometry says. Subgrades are never perfectly flat, forms bow slightly, some mix stays in the mixer and wheelbarrow, and a slab poured thin because you ran out is a slab that cracks. The industry habit is 5-10% extra — the waste field defaults to 10% and the result card shows both the net and waste-adjusted numbers so nothing is hidden.
Bags or a truck? Bagged mix makes sense up to roughly 1 cubic yard (about 45 × 80 lb bags — a full weekend of mixing). Beyond that, ready-mix delivery wins on both labor and consistency; a typical truck carries up to about 10 yd³ (7.6 m³). The calculator flags when your pour crosses into truck territory. Note that many suppliers charge a short-load fee for small deliveries, so mid-size pours (1-2 yd³) are worth pricing both ways — the optional price field accepts per-bag or per-volume rates.
One more distinction worth knowing: concrete is the cement-sand-gravel mix you pour; cement is just the grey powder that glues it together. Bagged "concrete mix" already contains the aggregate — you only add water.