Plaster calculator: cement and sand
Enter the wall area, the plaster thickness and the cement to sand ratio to see how much material to buy.
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How to use it
- Enter plaster area, coat thickness, mix ratio (cement:sand), dry volume factor and cement bag weight.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Wet volume = area × (thickness ÷ 1000). Dry volume = wet × factor (1.33). Cement = dry ÷ (1 + sand parts) × 1440 kg/m³; sand = dry × sand parts ÷ (1 + sand parts).
Example
Inputs: Plaster area = 50 m², Coat thickness = 12 mm, Mix ratio (cement:sand) = 1:6, Dry volume factor = 1.33, Cement bag weight = 50 kg. Result: Cement bags to buy: 4 bags; Cement weight: 164.2 kg; Sand: 0.684 m³.
Limits and caveats
- The 1.33 factor and 1440 kg/m³ cement density are common estimating values, so treat the result as an estimate.
- Uneven walls need a thicker coat, so enter the real average thickness.
Questions about this tool
How many cement bags to plaster 100 m² at 12 mm?
At 1:6 with the 1.33 factor you need about 328 kg, so 7 bags of 50 kg, plus roughly 1.37 m³ of sand.
What is a typical plaster thickness?
Commonly 12 to 15 mm on internal walls and 15 to 20 mm on external walls in two coats.
Why multiply by 1.33?
Dry sand and cement lose volume once water is added, and the factor covers that shrinkage plus some loss.