算BuildCalc

Mortar Calculator

Choose brickwork or plastering, enter area and thickness, and get mortar volume plus cement and sand quantities.

Quick answer

With the default inputs: Application Plastering mortar · Plaster area 100 m² · Plaster thickness 20 etc.Mortar volume 2.21 m³

Edit the inputs below to recalculate.
Length LHeight HThickness T
Area multiplied by the unit rate; joint thickness drives the required mortar consistency.

Inputs

m²
Ignored when masonry is selected
15-20 mm indoors, 20-25 mm outdoors
m³
%

Result

Mortar volume
2.21m³
Net volume2.10m³
With waste2.21m³
Cement (M7.5)507kg
Bags (50 kg)11bags
Sand2.25m³
Sand in tonnes3.37t
Water (approx.)254kg

Cement contents are reference values for common mixes; the approved mix design governs.

Formula

PlasteringV = area × thickness ÷ 1000 × 1.05 (uneven substrate)
BrickworkV = masonry volume × 0.26
With wasteV_total = V × (1 + waste %)
CementW = V_total × kg per m³ (M5 200 / M7.5 230 / M10 275 / M15 330)
SandV_sand = V_total × 1.02
100 m² of plaster at 20 mm: 2.1 m³ net, 2.21 m³ with 5% waste, needing about 508 kg of cement (11 bags) and 2.25 m³ of sand for M7.5.

How to work it out

  1. Establish whether you are pricing masonry or plaster — mortar per cubic metre of brickwork and per square metre of plaster are different calculations entirely.
  2. Masonry mortar: net per cubic metre is one minus the net brick volume, about 0.226 m³/m³ in a 240 mm wall, then apply 1.05 for joint fill.
  3. Plaster mortar: by thickness, typically 20 mm in two coats, about 0.02 m³ per square metre.
  4. Convert mortar volume to cement and sand from the mix: M5 takes about 200 kg cement and 1.15 m³ sand per cubic metre.
  5. Convert to bags at 50 kg and add 5% for site mixing loss.

Where it goes wrong

Material and cost

Dry-mixed masonry mortar is about 300-380 per tonne delivered, while site mixing works out around 250-330 per m³. An M5 cement mortar needs about 200 kg cement (90 at 450 per tonne) and 1.15 m³ sand (138 at 120 per m³), so material lands near 230 per m³ before labour. Dry mix saves labour but costs 20-30% more in material.

On site

Basis

FAQ

Why is brickwork mortar estimated at 26% of masonry volume?
That is the void ratio of standard brickwork. One cubic metre holds about 508 bricks occupying 0.74 m³, leaving 0.26 m³ of mortar in the joints. With perforated bricks or AAC blocks that drops to 10-15%.
Why multiply plaster area by 1.05?
Because substrates are never perfectly flat. Permitted deviation is 4-5 mm, and hollows need extra mortar, so add 5% on top of the theoretical thickness, or 10% for uneven older walls.
Which grade should I use, M5, M7.5 or M10?
Brickwork: M10-M15 below ground level, M7.5-M10 for load-bearing walls, M5 for partitions. Plastering: M5-M7.5 indoors, M10 or above outdoors and in wet areas. Over-specifying wastes cement and increases shrinkage cracking.

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Mortar Calculator. 2026-10-25. https://jianzhujisuan.com/en/mortar

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.