Concrete calculator
Calculate how much concrete you need for a slab, path, base or round column — in cubic metres or yards, bags of pre-mix, or cement, sand and gravel to mix yourself.
Your estimate
Concrete volume
0.95 m³
- Pre-mix bags
- 102
- Pre-mix weight
- 2,032 kg
- Cement (site mix)
- 299 kg
- Sand (site mix)
- 0.42 m³
- Gravel / aggregate (site mix)
- 0.83 m³
Estimates for planning only — not a quote, survey or financial advice.
How this is calculated
Formula
- Slab volume = length × width × thickness · column = π × (diameter ÷ 2)² × height
- Total = volume × number of pours × (1 + extra %)
- Pre-mix bags = total × yield density ÷ bag weight (rounded up)
- Site mix: dry volume = wet volume × 1.54; cement, sand and gravel split by the ratio; cement weight = cement volume × 1,440 kg/m³
Assumptions
- Yield density is how much dry pre-mix fills one cubic metre once mixed. 2,150 kg/m³ matches the common rule that an 80 lb bag makes about 0.6 ft³ — check the yield printed on your bag.
- The 1.54 dry-volume factor and 1,440 kg/m³ cement bulk density are common rules of thumb for nominal mixes, not a structural mix design.
- Foundations, suspended slabs, retaining walls and anything load-bearing need a design from a structural engineer and must meet local building regulations.