# Mortar Calculator

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

- Page: https://jianzhujisuan.com/en/mortar
- Category: Masonry (https://jianzhujisuan.com/en/c/masonry)
- Chinese version: https://jianzhujisuan.com/zh/mortar.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Application Plastering mortar (area × thickness), Plaster area 100 m², Plaster thickness 20 mm, Masonry volume 10 m³, Mortar grade M7.5, Waste allowance 5%): **Mortar volume 2.21 m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Application | select | Plastering mortar (area × thickness) | — |  |
| Plaster area | number | 100 | m² | Ignored when masonry is selected |
| Plaster thickness | number | 20 | mm | 15-20 mm indoors, 20-25 mm outdoors |
| Masonry volume | number | 10 | m³ |  |
| Mortar grade | select | M7.5 | — |  |
| Waste allowance | number | 5 | % |  |

## Formula

- **Plastering**: V = area × thickness ÷ 1000 × 1.05 (uneven substrate)
- **Brickwork**: V = masonry volume × 0.26
- **With waste**: V_total = V × (1 + waste %)
- **Cement**: W = V_total × kg per m³ (M5 200 / M7.5 230 / M10 275 / M15 330)
- **Sand**: V_sand = V_total × 1.02

## Worked example

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.

## Questions

### 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.

## Related tools

- [Brick Wall Calculator](https://jianzhujisuan.com/en/brick-count): Pick a wall thickness, enter length and height, deduct openings, and get brick count plus mortar volume.
- [AAC Block Quantity Calculator](https://jianzhujisuan.com/en/aac-block): Block count, volume and adhesive from wall size and block format.
- [Hollow Brick Quantity Calculator](https://jianzhujisuan.com/en/hollow-brick): Brick count, mortar volume and bricks per m³ from wall thickness and format.
- [Masonry Mortar Mix Calculator](https://jianzhujisuan.com/en/masonry-mortar-mix): Cement, sand and water for M5-M15 mortar by volume, with a batch sheet.
- [Masonry Tie Bar Calculator](https://jianzhujisuan.com/en/tie-bar): Tie bar count, weight, holes and resin from wall and spacing.
- [Tie Column Quantity Calculator](https://jianzhujisuan.com/en/tie-column): Tie column count, concrete, formwork and rebar from wall and section.

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