Concrete Calculator
Concrete Calculator
Enter the length and width of your slab or footing, plus its thickness in inches, to find the volume of concrete needed — shown in cubic feet, cubic yards (how ready-mix is typically ordered), and the number of 80 lb pre-mixed bags if you're buying bagged concrete instead.
Ready-mix trucks price and deliver concrete by the cubic yard, which is why the calculator converts the raw cubic-foot volume by dividing by 27 (the number of cubic feet in a cubic yard) — a 10×10 ft slab poured 4 inches thick works out to about 1.23 cubic yards, or roughly 56 bags if you're mixing it yourself from 80 lb bags instead of ordering a truck. Getting this number right before ordering matters more than it might seem: ready-mix suppliers often charge a short-load fee for orders under a minimum truck volume, so slightly underestimating can end up costing more than simply rounding up.
- Imperial formula: Volume = Length × Width × (Thickness ÷ 12), converted to cubic yards by dividing by 27. Example: a 10×10 ft slab at 4 inches = 33.3 cubic feet = 1.23 cubic yards ≈ 56 bags of 80 lb pre-mix.
- Metric formula: Volume = Length × Width × (Thickness ÷ 100), in cubic meters. Example: a 3×3 m slab at 10 cm = 0.9 m³ ≈ 72 bags of 25 kg pre-mix.
- Switch units using the Unit System selector — all figures recalculate instantly in either Imperial (ft, in, 80 lb bags) or Metric (m, cm, 25 kg bags).
Should I order ready-mix or use bagged concrete?
Ready-mix (ordered by the cubic yard) is usually more economical and consistent for anything over about 1 cubic yard; bagged concrete is more practical for small jobs.
Does this account for waste?
No — it's the exact geometric volume. Most contractors add 5-10% extra to cover spillage, uneven excavation, and minor form movement.
Concrete Calculator
Enter the length and width of your slab or footing, plus its thickness in inches, to find the volume of concrete needed — shown in cubic feet, cubic yards (how ready-mix is typically ordered), and the number of 80 lb pre-mixed bags if you're buying bagged concrete instead.
Ready-mix trucks price and deliver concrete by the cubic yard, which is why the calculator converts the raw cubic-foot volume by dividing by 27 (the number of cubic feet in a cubic yard) — a 10×10 ft slab poured 4 inches thick works out to about 1.23 cubic yards, or roughly 56 bags if you're mixing it yourself from 80 lb bags instead of ordering a truck. Getting this number right before ordering matters more than it might seem: ready-mix suppliers often charge a short-load fee for orders under a minimum truck volume, so slightly underestimating can end up costing more than simply rounding up.
- Imperial formula: Volume = Length × Width × (Thickness ÷ 12), converted to cubic yards by dividing by 27. Example: a 10×10 ft slab at 4 inches = 33.3 cubic feet = 1.23 cubic yards ≈ 56 bags of 80 lb pre-mix.
- Metric formula: Volume = Length × Width × (Thickness ÷ 100), in cubic meters. Example: a 3×3 m slab at 10 cm = 0.9 m³ ≈ 72 bags of 25 kg pre-mix.
- Switch units using the Unit System selector — all figures recalculate instantly in either Imperial (ft, in, 80 lb bags) or Metric (m, cm, 25 kg bags).
Should I order ready-mix or use bagged concrete?
Ready-mix (ordered by the cubic yard) is usually more economical and consistent for anything over about 1 cubic yard; bagged concrete is more practical for small jobs.
Does this account for waste?
No — it's the exact geometric volume. Most contractors add 5-10% extra to cover spillage, uneven excavation, and minor form movement.