Dry volume of mortar = wet volume × 1.33. For 1 m³ of 1:6 cement mortar the dry volume is 1.33 m³, which splits into 0.19 m³ of cement (5.47 bags of 50 kg) and 1.14 m³ of sand.
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Cement = 1.330 ÷ (1 + 6) = 0.190 m³ → ÷ 0.0347 m³ per bag = 5.47 bags
Sand = 1.330 × 6 ÷ 7 = 1.140 m³
Water = cement weight × 0.50
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Dry sand and cement contain air gaps, and sand also bulks when damp. Once water is added and the mortar is mixed, the cement fills the gaps between sand grains, so the wet mortar takes up less space. About 33% more dry material is needed, hence 1.33. Some estimators use 1.27 to 1.35.
Is the 1.33 factor given in an IS code?
No. It is an estimating convention from site practice and textbooks, not a clause of IS 456 or IS 2250. Use your own site's figure if you have measured it.
Why is mortar's factor smaller than concrete's 1.54?
Concrete has coarse aggregate with large gaps that the sand and cement fill, so its dry materials shrink more when mixed. Mortar has only sand and cement, so the reduction is smaller.
