What this calculates
This is the main Concrete Calc tool. It supports eleven project shapes — rectangular and square slabs, circular slabs and rings, footings, walls, columns, post holes, solid steps, tubes, round footings and curb & gutter — each with its own exact solid model and labelled diagram.
Every assumption is visible and editable: waste allowance, placed density, bag yield, and any prices you choose to enter. Nothing is estimated from hidden averages.
For a specific job, use one of the specialist calculators linked below — they reuse this same tested engine with the right shape preselected.
Formula
Rectangular: V = L × W × H × quantity
Round: V = π × (D ÷ 2)² × H × quantity
Ring / tube: V = π × [(D₁/2)² − (D₂/2)²] × H × quantity
Cubic yards = cubic feet ÷ 27
Worked example
12 × 16 ft shed base, 4 in thick
- 1.12 × 16 × 0.333 = 64 cu ft
- 2.64 ÷ 27 = 2.37 cu yd
- 3.Add 10% waste: about 2.61 cu yd to order
Common mistakes
- Mixing inches and feet in one multiplication — convert everything to the same unit first.
- Ordering the exact calculated volume with no waste allowance.
- Treating a volume estimate as structural design; thickness and reinforcement come from your plans or local code.
Frequently asked questions
How do I calculate how much concrete I need?
Multiply length × width × thickness in feet to get cubic feet, divide by 27 for cubic yards, then add 5–10% for waste. The calculator above does this for eleven shapes.
Can I switch between US and metric units?
Yes. Use the unit toggle and every dimension converts in place; results always show yd³, ft³, m³ and litres together.
Does the calculator include cost?
Optionally. Enter your own quoted price per cubic yard or metre, plus any delivery, labor or reinforcement costs — the tool never invents prices.