Calculate how much cement, sand and aggregate you need for a concrete slab, footing or pour. Choose your concrete mix grade (M10 through M25), enter the pour dimensions, and get the number of 50 kg cement bags along with sand and aggregate volumes.
Enter dimensions to calculate.
Cement calculation uses the dry volume method to account for the compaction of voids when materials are mixed with water:
Dry Volume = Wet Volume × 1.54
Cement (bags) = (Dry Vol × Cement Parts ÷ Total Parts) × Density ÷ 50 kg
The factor 1.54 accounts for the 54% increase in volume when dry ingredients fill voids that were not present in the mixed concrete. The bulk density of cement is approximately 1,500 kg/m³.
The numbers refer to the characteristic compressive strength in N/mm² at 28 days. M20 is the most common grade for residential construction in most countries.
Concrete is a mixture of cement, fine aggregate (sand) and coarse aggregate (gravel or crushed stone). For an M20 mix (1:1.5:3), every 1 part cement requires:
Always use clean, well-graded aggregates free from clay, organic matter and excessive fines. Impurities reduce concrete strength significantly.
Cement is the binding agent — a fine powder of calcium silicates. Concrete is cement mixed with sand, aggregate and water. You cannot pour "cement" — you pour concrete.
Approximately 8 bags (400 kg) of cement per cubic metre of M20 concrete, plus roughly 600 kg of sand and 1,200 kg of coarse aggregate.
Concrete achieves about 70% of its design strength at 7 days and full strength at 28 days. Keep it moist during curing to prevent cracking.