How this calculator works
Convert finished volume to a loose dry-material allowance using a factor from your mix design or trial batch. Divide that allowance among the volume parts, then convert loose cement volume to mass using its bulk density. The initial 1:2:3 ratio and 1.54 factor are estimating assumptions, not strength grades. Cement particle density is not the loose bulk density used here. Water is based on the cement actually needed, rather than all the cement in rounded purchase bags. Prices are in Canadian dollars.
Formula
Dry volume = wet volume x dry factor; allowance = dry volume x (1 + waste); cement volume = allowance x cement parts / total parts; cement mass = cement volume x bulk density; water mass = cement mass x water-cement ratio; bags = ceil(cement mass / bag mass).
Worked example
For 1 m3 wet volume, factor 1, no waste and a 1:2:3 mix, cement occupies 1/6 m3. At 1200 kg/m3 this is 200 kg, or eight 25 kg bags. A water-cement mass ratio of 0.5 calls for 100 kg of water before aggregate-moisture corrections.
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Frequently asked questions
Does a ratio guarantee concrete strength?
No. Strength also depends on cement, aggregates, water, compaction and curing. Use an approved mix design for structural work.
Why use a dry-volume factor?
Loose constituents contain voids that are reduced during mixing. The factor is specific to the materials and measured batch yield; 1.54 is only an initial planning assumption.
Can I use this water quantity directly?
Account for water carried by wet sand and gravel, absorption and admixtures. Follow the specified effective water-cement ratio rather than adding water solely for workability.