# Masonry Mortar Mix Calculator

Cement, sand and water for M5-M15 mortar by volume, with a batch sheet.

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

## Quick result

With the default inputs (Mortar volume 1 m³, Mortar grade M7.5, Cement class 32.5, Sand moisture 2%): **Cement 220 kg**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Mortar volume | number | 1 | m³ |  |
| Mortar grade | select | M7.5 | — |  |
| Cement class | select | 32.5 | — |  |
| Sand moisture | number | 2 | % |  |

## Formula

- **Cement**: M = reference by grade × volume
- **42.5 class**: reference × 0.88
- **Sand**: V = 1.02 × mortar volume (loose)
- **Water to add**: W = 280 × V − moisture in sand
- **Strength**: 70.7 mm cube at 28 days

## Worked example

1 m³ of M7.5 with 32.5 class cement and 2% sand moisture: 220 kg cement (5 bags), 1.02 m³ of dry sand around 1479 kg and about 250 kg of added water — a ratio near 1 : 6.7.

## Questions

### What does M7.5 mean?

A mean compressive strength of at least 7.5 MPa for 70.7 mm cubes cured 28 days. It is a mean, not a characteristic value, and the specimen is a 70.7 mm cube — not the 150 mm cube used for concrete. Mortar test results scatter far more than concrete.

### Why deduct the water in the sand?

Sand at 2% moisture brings about 30 kg of water per cubic metre; adding the full 280 kg pushes the water-cement ratio over 10% high, costing 15-20% strength and increasing shrinkage. In the rainy season sand can reach 8%. Measure moisture each shift by drying or a rapid meter.

### Is more cement always better in mortar?

No. Excess cement increases shrinkage and cracking, mismatches brick movement and costs more. The key property is workability — water retention and consistency — which lime putty or fly ash improve better than extra cement. The code sets a minimum cement content but also discourages over-strong mortar in masonry.

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Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.