Concrete Calculator
Cement bags, sand and aggregate for a slab, footing or beam — enter the dimensions and mix ratio.
No login required · M15, M20 and M25 mixes
Standard dry-volume-factor (1.54) estimate for planning quantities. Order 5–8% extra for wastage. Not a substitute for a structural design mix.
How this is calculated
Wet volume = Length × Width × Thickness. This is converted to a dry volume by multiplying by 1.54 — the standard allowance for the fact that loose dry materials (cement, sand, aggregate) occupy more space than the finished, compacted concrete they produce.
The dry volume is then split by the mix ratio. For M20 (1 : 1.5 : 3), the ratio has 5.5 total parts — cement gets 1/5.5 of the dry volume, sand gets 1.5/5.5, and aggregate gets 3/5.5. Cement volume is converted to bags using 1 bag = 50 kg = 0.0347 cum.
Common questions
How do you calculate cement, sand and aggregate for concrete?
Find the wet volume (length × width × thickness), multiply by 1.54 to get the dry volume, then split that by the mix ratio — for M20 (1:1.5:3), cement gets 1 part of 5.5 total, sand 1.5 parts, aggregate 3 parts.
How many bags of cement in 1 cubic metre of concrete?
For M20 (1:1.5:3), roughly 8 bags of 50kg cement per cubic metre of finished concrete. M15 uses fewer bags per cum; M25 uses more.
Why multiply by 1.54 for dry volume?
Wet concrete volume is less than the sum of its dry ingredients because sand and aggregate settle and cement fills the gaps between them. 1.54 is the standard factor used to convert a wet (poured) volume back to the dry material volume needed.
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