Cement Sand Calculator

Cement and sand quantities for plaster and mortar depend on the volume of the work, the mix ratio and the fact that dry materials shrink when water is added. This calculator converts your plaster area or mortar volume into the number of 50 kg cement bags and cubic metres of sand to order.

How to use it

1. Enter the plaster area and thickness, or the wet mortar volume.
2. Choose the mix ratio, for example 1:4 or 1:6 (cement : sand).
3. Read the cement in bags and kilograms and the sand in cubic metres.

The calculation

Wet volume = area × thickness. Dry volume = wet volume × 1.27, plus a small allowance for wastage and uneven surfaces (many engineers use a total factor of 1.33 to 1.35). Cement volume = dry volume × cement part / total parts. Bags = cement volume / 0.0347, because one 50 kg bag occupies about 0.0347 m³ at 1440 kg/m³.

Worked example

Plastering 100 m² at 12 mm thickness in 1:6 mix: wet volume = 100 × 0.012 = 1.2 m³. Dry volume = 1.2 × 1.27 = 1.524 m³, plus 20% for wastage and uneven surfaces = 1.83 m³. Cement = 1.83 / 7 = 0.261 m³ = 7.5 bags. Sand = 1.83 × 6 / 7 = 1.57 m³.

Typical mix ratios

• 1:3: repair work and ceiling plaster in some specifications.
• 1:4: external plaster and exposed brickwork.
• 1:5 to 1:6: internal plaster and general masonry mortar.

Tips

• Use clean, well-graded sand; silt weakens plaster.
• Cure plaster for at least 7 days to prevent cracking.