Mortar and Plaster Quantity Calculator

How much material does plastering need?

Start with the wet volume of plaster: area × thickness. A 2 cm coat on 100 m² of wall is 2 m³. A waste allowance covers droppings and what goes into uneven surfaces.

Sand and cement are measured loose and lose volume when mixed with water. The wet volume is therefore multiplied by a dry volume factor, about 1.3 for mortar in site practice. The dry volume is then shared out by the mix ratio:

cement volume = dry volume × c / (c + s), sand volume = dry volume × s / (c + s)

The cement volume becomes kilograms through the bulk density (about 1440 kg/m³) and bags through the bag weight.

Example

100 m², 2 cm thick, 10 percent waste, 1 : 4 mix: wet volume 2.2 m³, dry volume 2.86 m³. Cement 2.86 / 5 × 1440 = 824 kg, which is 17 bags. Sand 2.29 m³.

Masonry mortar

If you already know the mortar volume of a brick or block wall, enter it directly on the second tab. The calculation is the same.

Premixed plaster

For bagged plaster the manufacturer gives consumption in kilograms per square metre per millimetre. The product needed is consumption × area × thickness. Gypsum, cement based and machine applied plasters differ widely, so always use the figure from the product data sheet.

Limits

The result is approximate. The factor depends on the sand and its moisture. The tool does not recommend a mix ratio and gives no water quantity.