Why is the dry volume larger than the wet (wall) volume?

Dry cement and sand particles have air gaps between them. When mixed with water they settle and bind together, shrinking in volume. The 1.33× dry volume factor accounts for this so you buy enough dry material to produce the wet volume you actually need.

Does this calculator cover ceiling plastering too?

It works for any flat surface, ceiling included, just enter the ceiling's area as the wall area. It doesn't distinguish wall from ceiling internally.

Plaster Quantity Calculator

Calculate cement and sand needed for wall plastering.

How this is calculated

Wet volume = area × thickness. Dry volume = wet × 1.33. Cement/sand split by mix ratio.

Assumptions used in this calculation

Dry volume factor: Uses a standard 1.33× bulking allowance for wet-to-dry mortar volume conversion.

About this calculator

Calculates the wet and dry mortar volume needed to plaster a wall at a given thickness, then splits it into cement bags and sand volume by mix ratio.

Worked example

50 sqm wall, 12mm thick, 1:4 mix

Result: 5 cement bags needed

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Frequently asked questions

Why is the dry volume larger than the wet (wall) volume?

Does this calculator cover ceiling plastering too?

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