How it is calculated
Thickness is converted from millimetres into metres, and the volume is multiplied by the density of the dry mix. Makers print the use per 10 mm on the bag. If you know it, enter your own density, or take the mass as area × centimetres × kilograms per m².
Volume = area × thickness in meters
Where the numbers come from
- Area — unit in the field: m²
- Thickness — unit in the field: mm
- Density — unit in the field: kg/m³
- Bag — unit in the field: kg
- Waste — unit in the field: %
Example
20 m² at a thickness of 50 mm. The volume is 1 m³. At 1 800 kg/m³ with 5% waste that is 1 890 kg, or 76 bags of 25 kg.
Questions
What is the default density?
1 800 kg/m³ is a common figure for a cement-and-sand mix. A light levelling compound prints a lower number on the bag. Enter that one.
Why the extra?
An uneven floor, and what stays in the tub. 5% is a modest allowance; on a crooked base, allow more.
Is this mixed mortar or a dry mix?
The mass is calculated as a dry mix of the density you set. For the mixing water, read the pack.