Cement Calculator
Estimate cement bags, sand, and aggregate from slab size and a mix ratio.
Enter your values and calculate to see the result.
Formula used
wet volume (m³) = length × width × thickness
dry batch volume (m³) = wet volume × 1.54
cement volume = dry × (cement parts / total parts)
cement mass = cement volume × 1440 kg/m³
sand / aggregate mass = their volume × 1600 / 1500 kg/m³
water (kg) = cement mass × 0.5
bags (50 kg) = ceil(cement mass / 50)
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Worked example
Slab: 10 ft × 10 ft × 4 in Ratio: 1:2:4
Wet: 2.54 m × 2.54 m × 0.102 m ≈ 0.658 m³
Dry: 0.658 × 1.54 ≈ 1.013 m³ Cement vol: 1.013 × (1/7) ≈ 0.145 m³
Cement mass: 0.145 × 1440 ≈ 208 kg → 5 × 50 kg bags
Sand: 1.013 × (2/7) × 1600 ≈ 463 kg Aggregate: 1.013 × (4/7) × 1500 ≈ 869 kg
Frequently asked questions
Why is the dry volume larger than the finished slab?
When you measure loose dry materials (cement, sand, aggregate) they contain air and sit less densely than the finished, compacted slab. Estimators multiply the finished volume by about 1.54 to get the dry batching volume — this calculator applies that factor, then weighs each material by its own bulk density.
What does a 1:2:4 mix ratio mean?
It is the proportion of cement to sand to coarse aggregate by volume — one part cement, two parts sand, four parts aggregate. A richer mix (more cement, e.g. 1:1.5:3) is stronger but uses more cement per cubic metre. You can type any ratio, not just the presets.
How much water do I need?
This calculator estimates water at a 0.5 water-to-cement mass ratio, which suits these grades. Real water demand depends on aggregate moisture, slump, and weather, so treat it as a starting point and adjust on site.
Should I use this or the concrete calculator?
Use this when you batch your own mix from cement, sand, and aggregate and need those separate quantities. Use the concrete calculator when you are buying pre-mixed bags or ordering ready-mix by the cubic yard.