# Mortar Mix Design Calculator

Trial strength, cement, water and sand, and the mix by mass.

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

## Quick result

With the default inputs (Mortar grade 10 MPa, Measured cement strength 42.5 MPa, Water-cement ratio 0.65, Sand bulk density 1.45 kg/L): **Cement content 210 kg/m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Mortar grade | number | 10 | MPa | Enter 5 for M5, 10 for M10 |
| Measured cement strength | number | 42.5 | MPa | 32.5 grade enters 32.5 |
| Water-cement ratio | number | 0.65 | — | 0.6-0.7 for a 50-70 mm flow |
| Sand bulk density | number | 1.45 | kg/L |  |

## Formula

- **Trial strength**: fm,o = k × f2 with k from 1.00 to 1.25
- **Cement**: Qc = 1000(fm,o + 15.09) ÷ (3.03 fce)
- **Water**: Qw = Qc × w/c
- **Sand**: Qs = (1000 − Qc/3.10 − Qw) × ρs
- **Mix by mass**: cement : sand = 1 : Qs/Qc
- **k values**: 1.25 for M5-7.5, 1.20 for M10, 1.15 for M15

## Worked example

M10 mortar with 42.5 cement at w/c 0.65 and 1.45 kg/L sand: trial strength 12.00 MPa, 210 kg/m³ of cement, 137 kg of water and 1153 kg of sand — a 1:5.49 mix, or 274 kg of sand per 50 kg bag.

## Questions

### Why not size mortar with a water-cement ratio formula?

Because mortar has no coarse aggregate, so its strength comes from the cement paste binding the sand — a different mechanism from concrete, where Bolomey's formula would be far off. JGJ/T 98 uses a statistical regression tying cement strength directly to the target, which matches trial results better on site. Trials still govern.

### Is a 1:3 volume mix good enough?

Workable, but understand that its strength is uncertain. Volume batching lets the cement content swing between 350 and 450 kg/m³ as the sand bulks and wets, which is a whole grade of strength. Proper practice is weighing — especially for load-bearing masonry and large plaster areas, where volume batching is the main cause of scatter.

### Does higher cement grade mean less cement?

Yes, but only down to a floor — usually 200 kg/m³. Below that the mortar loses workability and water retention: it will not hang on a trowel or a block, and plaster crazes. So a 52.5 cement for M5 computes at 120 kg but must be raised to 200 with fly ash or lime to restore workability, or the saving costs the quality.

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