Concrete Calculator
Enter slab or footing dimensions and instantly see cubic yards, cubic meters, and number of 40/60/80 lb bags needed with a 10% waste allowance.
How to use Concrete Calculator
The concrete calculator estimates the volume of concrete needed for slabs, footings, columns, steps and circular pads. Enter the dimensions and it returns cubic yards and cubic metres, the number of 60 lb or 80 lb bags, and an estimated material cost — so you can order exactly what you need without waste or a costly second delivery.
- Choose the shape: slab, footing, column or circular.
- Enter length, width (or diameter) and depth/thickness.
- Add a waste factor (typically 10%).
- Review volume in cubic yards, number of bags and estimated cost.
Your data never leaves your device — 100% private processing.
How concrete volume is calculated
Volume (cu yd) = Length (ft) × Width (ft) × Depth (ft) ÷ 27. One cubic yard weighs about 4,000 lbs. Coverage from bags: a 60 lb bag yields 0.45 cu ft; an 80 lb bag yields 0.60 cu ft. Always add 10% for waste and spillage. Pre-mixed ready-mix concrete is ordered by the cubic yard and is cost-effective for pours over about 1 cubic yard.
| Bag size | Yield | Bags per cu yd | Approx. cost/bag |
|---|---|---|---|
| 60 lb | 0.45 cu ft | 60 bags | ~$5–7 |
| 80 lb | 0.60 cu ft | 45 bags | ~$6–9 |
| 90 lb (rapid-set) | 0.67 cu ft | 40 bags | ~$8–11 |
Mix ratios and concrete strength
Standard residential concrete is 3,000–4,000 PSI compressive strength, achieved with a water:cement ratio of about 0.45–0.55. The classic mix is 1 part cement : 2 parts sand : 3 parts aggregate (by volume). Adding more water weakens the mix; reducing aggregate increases strength and workability. For driveways and garage slabs, 4,000 PSI minimum is recommended.
Glossary
- Cubic yard
- 27 cubic feet — the standard unit for ordering ready-mix concrete.
- PSI
- Pounds per square inch — the compressive strength of cured concrete.
- Water-cement ratio
- The weight of water divided by the weight of cement; lower = stronger.
- Slump
- A measure of fresh concrete workability; standard residential slump is 4–5 inches.
Related reading
Frequently Asked Questions
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Why use Concrete Calculator?
- Accurate material estimates reduce waste and over-ordering
- Supports both metric and imperial measurements
- Covers common materials: concrete, lumber, flooring, paint
- Results include waste factor buffers for professional accuracy
Common use cases
- Calculate concrete needed for a driveway
- Estimate flooring tiles for a room renovation
- Work out paint quantity for interior walls
- Calculate lumber needs for a deck project
- Estimate roofing material for a pitched roof
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