# Floor Screed Material Calculator

Volume to cement, sand and water by mix ratio.

- Page: https://jianzhujisuan.com/en/floor-screed
- Category: Finishes (https://jianzhujisuan.com/en/c/finishes)
- Chinese version: https://jianzhujisuan.com/zh/floor-screed.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Area 100 m², Thickness 30 mm, Mix ratio (by volume) Cement mortar 1:3 (strong, wearing), Waste 5%): **Mortar volume 3.15 m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Area | number | 100 | m² |  |
| Thickness | number | 30 | mm |  |
| Mix ratio (by volume) | select | Cement mortar 1:3 (strong, wearing) | — |  |
| Waste | number | 5 | % |  |

## Formula

- **Volume = area × thickness**: divide mm by 1000
- **Cement = per m³ (by mix) × volume**: 400 / 320 / 270 / 230 kg
- **Sand = per m³ × volume**: 0.45-0.50 m³/m³
- **Water ≈ cement × 0.6**: w/c about 0.6

## Worked example

100 m² at 30 mm with 1:4 mortar: 3.00 m³, 3.15 m³ with 5% waste; cement 1.01 t (21 bags), sand 1.48 m³ (about 2.22 t) and roughly 0.61 m³ of water.

## Questions

### Why does screed go hollow and crack?

Four causes: a dirty or unwetted base sucking water out of the mortar and killing bond; too rich a mix shrinking more; too thin a layer (under 20 mm) or over-trowelling that densifies the surface while the core stays weak; and no curing. Codes require at least 20 mm, movement joints in large areas, and water curing from 24 hours for at least 7 days.

### Can self-levelling replace sand-cement screed?

It depends. Self-levelling is flat, fast and thin (3-10 mm) - ideal under wood, carpet or vinyl - but weak and water-sensitive, so not for wet areas or as a wearing surface. Sand-cement is strong and water resistant but thicker, slower to cure and dependent on the trowel. A common combination is screed for bulk then self-levelling for finish.

### 1:3 or 1:4?

Depends on exposure. 1:3 is strong and abrasion resistant, suitable as a wearing surface (garages, warehouses) or under tiles where load matters; 1:4 is the general screed mix - adequate strength, less shrinkage, easier to work; 1:5 and 1:6 are bedding only. More cement is not stronger in practice: 1:2 or 1:1 shrinks so much it cracks and debonds.

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