Concrete Calculator
Estimate how much concrete you need for common shapes (slab, footing, or round column) and see the result in cubic yards, cubic metres, and premixed bags.
| Shape | |
| Length | |
| Width | |
| Diameter | |
| Thickness / height | |
| Quantity | pieces |
Result
Your concrete estimate will appear here.
Formula and assumptions
- Slab/footing volume = length × width × thickness (in consistent units).
- Column volume = π × (diameter/2)² × height.
- 1 cubic yard = 27 cubic feet. Bag counts are approximate (a 60 lb bag yields ~0.45 cu ft, an 80 lb bag ~0.60 cu ft).
- This is an estimate. It does not add waste automatically — consider ordering about 5–10% extra for spillage, uneven subgrade, and over-excavation.
How it works
Concrete needed is the volume of the space you’re filling. This calculator estimates volume for common shapes and converts it to ordering units.
Formulas
- Slab/footing: Volume = length × width × thickness
- Round column: Volume = π × (diameter/2)² × height
- 1 cubic yard = 27 cubic feet. Bag yields are approximate (≈0.45 ft³ for 60 lb, ≈0.60 ft³ for 80 lb premix).
Worked example
A 10 ft × 10 ft slab, 4 inches thick: volume = 10 × 10 × (4/12) = 33.33 ft³ = about 1.23 yd³ (≈75 of 60 lb bags or ≈56 of 80 lb bags).
Assumptions & tips
- Order about 5–10% extra for spillage, uneven subgrade, and over-excavation. Reinforcement, sub-base, and curing are not calculated here.
- Confirm mix type and quantities with your supplier or contractor.
Estimate only. Actual material needs vary by site conditions and mix.
How to use the Concrete Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Pick the shape.
- Enter the length.
- Enter the width.
- Enter the diameter.
- Enter the thickness / height.
- Enter the quantity.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Concrete Calculator — frequently asked questions
What formula does the Concrete Calculator use?
Slab/footing volume = length × width × thickness (in consistent units). Column volume = π × (diameter/2)² × height. 1 cubic yard = 27 cubic feet. Bag counts are approximate (a 60 lb bag yields ~0.45 cu ft, an 80 lb bag ~0.60 cu ft). This is an estimate. It does not add waste automatically — consider ordering about 5–10% extra for spillage, uneven subgrade, and over-excavation.
How does the Concrete Calculator work?
Concrete needed is the volume of the space you’re filling. This calculator estimates volume for common shapes and converts it to ordering units.
What assumptions and limitations should I know about?
Order about 5–10% extra for spillage, uneven subgrade, and over-excavation. Reinforcement, sub-base, and curing are not calculated here. Confirm mix type and quantities with your supplier or contractor.
Can you walk through a worked example?
A 10 ft × 10 ft slab, 4 inches thick: volume = 10 × 10 × (4/12) = 33.33 ft³ = about 1.23 yd³ (≈75 of 60 lb bags or ≈56 of 80 lb bags).
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.