Concrete Calculator
Enter the size of your slab, footing or beam and the concrete grade — get the cement bags, sand and aggregate you need, with the standard 1.54 dry-volume factor already applied.
How the concrete calculator works
Concrete is measured by volume. The dry ingredients take up more space than the finished concrete, so we multiply the wet volume by 1.54 to get the dry volume, then divide it in the grade's cement : sand : aggregate ratio.
- Wet volume = length × width × depth
- Dry volume = wet volume × 1.54
- Cement = dry volume × (cement part ÷ total parts); 1 bag (50 kg) ≈ 0.0347 m³
- Sand & aggregate = dry volume × their parts ÷ total parts
Common grades (cement : sand : aggregate)
| Grade | Ratio | Typical use |
|---|
| M10 | 1 : 3 : 6 | Levelling / PCC base |
| M15 | 1 : 2 : 4 | Footings, flooring |
| M20 | 1 : 1.5 : 3 | Slabs, columns, beams (low-rise) |
| M25 | 1 : 1 : 2 | Heavily loaded members |
Planning tool only. For structural work always follow your engineer's design mix and a proper BOQ.
Concrete calculator FAQ
How many bags of cement in 1 m³ of M20 concrete?›
For M20 (1:1.5:3), about 8 bags of 50 kg cement per cubic metre of concrete, using the 1.54 dry-volume factor.
Should I add wastage?›
Yes — add roughly 3–5% to cover spillage, uneven formwork and handling losses on site.
Can I use this for ready-mix (RMC)?›
Use it to estimate the volume to order. RMC is billed per cubic metre, so the wet volume figure here is what you need.