How mortar volume is calculated
Volume is simply the area to cover times how thick you spread the mortar. Since 1 m² covered 1 mm deep equals exactly 1 liter, multiplying area (m²) by thickness (mm) gives liters directly.
- width — wall or floor width in meters
- length — wall or floor length in meters
- thickness — plaster/mortar coat thickness in millimeters
More detail
Why no fixed thickness constant
Plaster thickness isn't a fixed standard — it depends on the surface, the mortar type, and the finish you want (a thin skim coat vs. a leveling coat on an uneven wall). Enter the thickness your job actually calls for rather than relying on a built-in default.
1 m² × 1 mm = 1 liter
A square meter covered to a depth of 1 millimeter holds exactly 1 liter (0.001 m³ × 1,000 L/m³ = 1 L). That's why area in m² multiplied directly by thickness in mm gives liters with no extra conversion factor.
Practical tip. Bagged mortar is usually sold by weight, not volume — check the bag for its yield in liters per bag (or per kg) and divide your total liters by that to estimate bags needed. Buy a bit extra to cover waste and uneven surfaces.
Frequently asked questions
How much mortar do I need for a 4m × 5m wall at 10mm thick?
20 m² × 10 mm = 200 liters (0.2 m³). Enter width 4, length 5, and thickness 10 above to see this computed directly.
Why does area (m²) times thickness (mm) give liters?
Because 1 m² covered 1 mm deep is exactly 0.001 m³, and 1 m³ equals 1,000 liters — the two conversions cancel out, so area (m²) × thickness (mm) equals volume in liters with no extra multiplier.
What plaster thickness should I use?
This calculator doesn't assume one — thickness depends on your surface and mortar type, typically a thin few millimeters for a skim coat up to 15–20mm for leveling an uneven wall. Check your mortar product's spec sheet or ask your contractor.
How do I convert the liters to bags of mortar?
Check the mortar bag's stated yield in liters (many list liters or kg per bag), then divide the "Mortar needed" figure above by that per-bag yield and round up. Bag yields vary by brand and mix ratio.