Example 1 — Render 20 m²
- thickness 15 mm
- 1800 kg/m³, +5% waste
567 kg
This is a simple scenario that helps estimate the material scale for basic masonry or repair work.
Mortar requirement calculator
Mortar mass from area × thickness × density, minus openings, plus waste %.
Also useful: cement in mortar, mortar bags needed.
Results
Enter data and click Calculate.
How the results are calculated
Net area = area − openings. Volume (m³) = net area × thickness. Mass (kg) = volume × density × (1 + waste/100).
How to use this calculator
- Enter area and layer thickness.
- Optionally subtract openings.
- Pick a mortar type or enter a custom density.
- Set waste % and Calculate to see mass and volume.
Usage examples
Example 2 — Wall with openings
- 50 m² − 5 m² openings
- 10 mm, 1600 kg/m³, +10%
792 kg
With a larger amount of mortar, it is worth looking not only at volume but also at how the material will be mixed and supplied.
Example 3 — Lightweight coat
- 15 m² × 20 mm
- 1500 kg/m³, +5%
472.5 kg
This example shows that even when the number seems small, mortar is still better calculated in advance than reordered later.
Frequently asked questions
How is mortar requirement calculated?
Net area (area minus openings) × thickness = mortar volume in m³; volume × density = mass in kg, then × (1 + waste%). Example: 20 m² × 15 mm, 1800 kg/m³ → 540 kg, +5% → 567 kg.
Which density should I choose?
Cement-lime mortar ~1800 kg/m³, cement mortar ~1600 kg/m³, lightweight ~1500 kg/m³, heavy screed ~2000 kg/m³. Pick the closest or enter a custom value.
Why subtract openings?
Door and window openings, or large unplastered areas, don't need mortar — subtract their area first.
What thickness should I use for plaster?
Typical render/plaster coats are 10–20 mm; masonry bedding joints are usually 10–12 mm.
Can I override the density?
Yes, enter a custom value in the density field — it takes priority over the type preset.
How do I switch metric ↔ US units?
Use the units selector in the header. Field labels, results and examples update automatically when you switch metric ↔ US.
Why do units matter so much here?
Because it is easy to confuse litres, kilograms, cubic metres, or bags, and that kind of mistake quickly ruins the purchasing estimate.
Should mortar be calculated with reserve?
Most often yes, especially when the substrate or site conditions are less predictable.