Concrete Calculator
Enter the dimensions of your slab, column or footing and the concrete calculator returns the volume in cubic meters and cubic yards, plus the number of bags to buy.
Volume in cubic meters
0.17 m³
Volume in cubic yards
0.222 yd³
Recommended order with 10% margin
0.187 m³ (0.244 yd³)
Covers spillage, uneven ground and slight over-digging. Running short mid-pour costs far more than the extra bag.
Examples
How to use
- 1
Pick the shape you are pouring: slab, column or footing.
- 2
Choose metric or imperial units, then enter the dimensions.
- 3
Set the quantity if you pour several identical elements.
- 4
Read the volume in m³ and yd³, the 10% margin and the bag count.
How the concrete calculator works
The concrete calculator covers the three shapes behind most home pours. Each one runs on a simple geometric formula:
- Slab and footing: length x width x thickness
- Column: pi x (diameter / 2)² x height
In metric mode every field is in meters, so a 10 cm slab goes in as 0.1. In imperial mode length, width, diameter and height are in feet, while thickness stays in inches. The calculator turns those inches into feet for you, which is where most hand estimates fall apart.
A worked example
Say you are pouring a patio slab of 4 m by 3 m at 10 cm thick. The volume is 4 x 3 x 0.1 = 1.2 m³, about 1.57 cubic yards. With the recommended 10% margin you would order 1.32 m³. In bagged concrete that comes to 110 bags of 25 kg, a clear sign that ready-mix delivery makes more sense at this size.
The same math holds in imperial units. A 12 x 10 ft slab at 4 inches is 12 x 10 x 0.333 = 40 cubic feet, or 1.48 cubic yards, since a cubic yard is 27 cubic feet.
Bags or a ready-mix truck?
The calculator shows both bag counts because the break-even point comes up fast. One 25 kg bag yields roughly 0.011 m³ of concrete once mixed, and a US 80 lb bag about 0.60 ft³ (0.017 m³).
| Volume needed | 25 kg bags | 80 lb bags | Best option |
|---|---|---|---|
| 0.1 m³ (small footing) | 10 | 6 | Bags |
| 0.5 m³ (short walkway) | 46 | 30 | Bags, with help |
| 1.2 m³ (4 x 3 m slab) | 110 | 71 | Ready-mix truck |
| 3 m³ (driveway) | 273 | 177 | Ready-mix truck |
Past roughly one cubic yard (0.76 m³), mixing by hand turns into a race against setting time. Ready-mix costs more per cubic meter, but it arrives as one consistent batch.
Why the 10% margin matters
Ground is never perfectly level, forms flex a little, and some concrete always clings to the mixer or the wheelbarrow. Order the exact computed volume and you finish the pour short, then pay far more for a second small delivery than the extra 10% would have cost. The calculator lists the margin on its own line so you can decide, and for slabs on grade you should almost always take it.
Typical slab thicknesses
A garden shed base works at 8 cm (3 in), a patio or garage floor at 10 cm (4 in), and a driveway that carries vehicles at 12 to 15 cm (5 to 6 in). Doubling the thickness doubles the volume, so check this value before anything else.
Parameters
Every field of this tool can be prefilled from the URL. Use these query parameters:
| Parameter | Type | Default |
|---|---|---|
| shape | slab | column | footing | slab |
| length | number | 4 |
| width | number | 3 |
| thickness | number | 0.1 |
| diameter | number | 0.3 |
| height | number | 2.4 |
| quantity | number | 1 |
| unit | metric | imperial | metric |
Example : https://www.veltotools.com/math/concrete-calculator?shape=slab&length=4&width=3&thickness=0.1
API
The same tool is available as a free JSON API, with the same parameters as above. No key, no sign-up.
Frequently asked questions
Updated Jul 17, 2026