Floor Screed Material Calculator
Volume to cement, sand and water by mix ratio.
Inputs
Result
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 |
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.
FAQ
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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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.