Free Online Calculators
Calculate material & drying time
This screed calculator works out the material in kg, the days until the screed is walkable and ready to cover, and the maximum residual moisture, from area, thickness, screed type and underfloor heating. Cement screed uses 21 kg per m² per cm and one week of drying per cm up to 4 cm: 25 m² at 6 cm needs 3,150 kg and 56 days.
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Multiply the floor area by the thickness. The calculator on this page does it in kilograms: area × thickness in cm × 21 kg for cement screed (20 kg for anhydrite or flow screed), so 25 m² at 6 cm needs 3,150 kg of dry material. If you mix your own sand and cement, convert the volume with your mix ratio instead, and add a small allowance for waste, uneven substrates and falls to drains.
A traditional sand and cement screed is mixed by volume with sharp sand making up the bulk and cement the smaller share, using only enough water for a damp, semi-dry consistency. Stronger ratios are used for heavy-duty floors, and additives or fibres can be added for thin or heated screeds.
The workable thickness depends on the type: bonded screeds are laid thinnest, unbonded screeds need more depth, and floating screeds over insulation or underfloor heating need the most. Going thinner than the manufacturer's minimum risks cracking, while excess depth slows drying and adds load to the structure.
The most common mistakes are adding too much water, poor substrate preparation, skipping the primer or damp-proof membrane, and failing to compact the screed properly. Rushing drying with heat or draughts, and omitting movement joints, also lead to curling and cracking.
Yes, provided the concrete is sound, clean, free of dust, laitance and contaminants, and prepared with a suitable bonding primer or slurry. If the concrete is weak, damp or unsuitable for bonding, lay the screed unbonded over a membrane instead.
Typical problems are cracking, curling at edges and joints, hollow or debonded areas, dusty or soft surfaces, and residual moisture that delays floor coverings. Most trace back to a poor mix, inadequate compaction, weak bonding or drying that was too fast or too slow.
Alternatives include self-levelling compounds for thin corrections, flowing anhydrite or calcium sulfate screeds, dry screed boards from gypsum fibre or chipboard, and a power-floated concrete slab finished as the wearing surface. The choice depends on depth available, drying time and the floor covering you plan to lay.
Planning a new floor? Before the screed goes down you want to know how much material to order and when you can lay the floor covering. This free screed calculator takes the area, thickness, screed type and underfloor heating and shows the material in kg, the date from which the screed is walkable, the date it is ready to cover and the maximum residual moisture before covering.
The material is area × thickness in cm × a material factor: 21 kg per m² and cm for cement screed, 20 kg for anhydrite and flow screed, 14 kg for dry screed. The calculator does not show a volume in m³, tonnes, or a split into cement, sand and water. Room temperature, humidity and ventilation are not inputs.
For cement screed the calculator uses the rule of thumb of one week (7 days) per centimetre up to 4 cm; beyond that the time grows with the square of the extra thickness: 28 days + (thickness − 4)² × 7. Anhydrite and flow screed follow the same logic with 5 days per centimetre. Underfloor heating adds 14 days. The screed counts as walkable after 15 % of the drying time, at least one day; dry screed is ready to cover immediately.
| Thickness | Cement kg/m² | Cement days to cover | Anhydrite/flow kg/m² | Anhydrite/flow days |
|---|---|---|---|---|
| 3 cm | 63 | 21 | 60 | 15 |
| 4 cm | 84 | 28 | 80 | 20 |
| 5 cm | 105 | 35 | 100 | 25 |
| 6 cm | 126 | 56 | 120 | 40 |
| 7 cm | 147 | 91 | 140 | 65 |
The values assume no underfloor heating and normal indoor conditions, around 15–22 °C with good ventilation. Cool or humid rooms slow drying considerably, so always measure residual moisture before laying a covering.
The calculator shows the maximum residual moisture in CM-%, measured with the calcium carbide (CM) method. It depends on screed type and heating: cement screed 2.0 CM-% unheated and 1.8 CM-% heated, anhydrite and flow screed (calcium sulfate) about 0.5 CM-% unheated and 0.3 CM-% heated. These are the usual readiness values of the German interface coordination for heated floor constructions (Schnittstellenkoordination); for heated calcium sulfate screed, 0.5 CM-% is sometimes quoted as well. The calculator treats flow screed as calcium sulfate based; for cement-based flow screed, the cement values apply. Your floor layer and the manufacturer have the final say.
The most widely used type: strong, moisture resistant, suitable indoors and outdoors and over underfloor heating. It dries the slowest.
Also known as calcium sulfate screed, it is usually pumped and self-levelling, conducts heat well and suits underfloor heating. It is sensitive to moisture and not suitable for permanently wet areas.
Dry screed boards made from gypsum fibre or wood-based panels are laid without water and can be covered immediately, but need a level, carefully prepared subfloor.
A 25 m² living room gets 6 cm of cement screed without underfloor heating, finished with tiles. The calculator shows 3,150 kg of material (25 × 6 × 21 kg), walkable after 8 days, ready to cover after 56 days and a maximum residual moisture of 2.0 %. At 5 cm the drying time drops to 35 days. With hot-water underfloor heating and the thickness left empty, it uses 4.5 cm: 2,363 kg and 44 days.
It depends on the thickness. At 5 cm the calculator uses 21 kg per m² and cm for cement screed, so 105 kg per square metre; anhydrite and flow screed come to 100 kg.
With the calculator's rule of thumb, cement screed needs one week per centimetre up to 4 cm and more beyond that: 35 days at 5 cm, 56 days at 6 cm. Before tiling the calculator shows a maximum of 2.0 % residual moisture; always measure before covering.
Light foot traffic is often possible after one to three days. The calculator is more cautious and uses 15 % of the drying time, at least one day: 4 days for 3.5 cm of cement screed. Avoid heavy loads until the screed has cured.
Yes. Choose the heating type: with the thickness field empty the calculator adds 1 cm (hot water) or 0.5 cm (electric) to the minimum and adds 14 days to the drying time. It does not check the required cover over the pipes, so enter your planned thickness yourself.
The calculator's defaults are 3.5 cm for cement, 3.0 cm for anhydrite, 2.5 cm for flow and 2.0 cm for dry screed. Floating screeds and screeds over heating pipes usually need more; follow your design and the manufacturer's data.