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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.

Units
ft
ft
in
%
lb
lb/ft³

Fields marked “example” are pre-filled with example assumptions, not verified current prices. Replace them with your own figures.

Your estimate

Concrete volume

1.3 yd³

Pre-mix bags
59
Pre-mix weight
4,698 lb
Cement (site mix)
692 lb
Sand (site mix)
0.57 yd³
Gravel / aggregate (site mix)
1.14 yd³

Estimates for planning only — not a quote, survey or financial advice.

How this is calculated

Formula

  1. Slab volume = length × width × thickness · column = π × (diameter ÷ 2)² × height
  2. Total = volume × number of pours × (1 + extra %)
  3. Pre-mix bags = total × yield density ÷ bag weight (rounded up)
  4. 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.